diff --git a/src/main/scala/gitbucket/core/api/ApiMilestone.scala b/src/main/scala/gitbucket/core/api/ApiMilestone.scala
new file mode 100644
index 0000000..4126c77
--- /dev/null
+++ b/src/main/scala/gitbucket/core/api/ApiMilestone.scala
@@ -0,0 +1,51 @@
+package gitbucket.core.api
+
+import gitbucket.core.model.{Milestone, Repository}
+import gitbucket.core.util.RepositoryName
+import java.util.Date
+
+/**
+ * https://docs.github.com/en/rest/reference/issues#milestones
+ */
+case class ApiMilestone(
+  url: ApiPath,
+  html_url: ApiPath,
+//  label_url: ApiPath,
+  id: Int,
+  number: Int,
+  state: String,
+  title: String,
+  description: String,
+  creator: ApiUser,
+  open_issues: Int,
+  closed_issues: Int,
+//  created_at: Option[Date],
+//  updated_at: Option[Date],
+  closed_at: Option[Date],
+  due_on: Option[Date]
+)
+
+object ApiMilestone {
+  def apply(
+    repository: Repository,
+    milestone: Milestone,
+    user: ApiUser,
+    open_issue_count: Int = 0,
+    closed_issue_count: Int = 0
+  ): ApiMilestone =
+    ApiMilestone(
+      url = ApiPath(s"/api/v3/repos/${RepositoryName(repository).fullName}/milestones/${milestone.milestoneId}"),
+      html_url = ApiPath(s"/${RepositoryName(repository).fullName}/issues?milestone=${milestone.title}&state=open"),
+//      label_url = ApiPath(s"/api/v3/repos/${RepositoryName(repository).fullName}/milestones/${milestone_number}/labels"),
+      id = milestone.milestoneId,
+      number = milestone.milestoneId, // use milestoneId as number
+      state = if (milestone.closedDate.isDefined) "closed" else "open",
+      title = milestone.title,
+      description = milestone.description.getOrElse(""),
+      creator = user,
+      open_issues = open_issue_count,
+      closed_issues = closed_issue_count,
+      closed_at = milestone.closedDate,
+      due_on = milestone.dueDate
+    )
+}
diff --git a/src/main/scala/gitbucket/core/controller/ApiController.scala b/src/main/scala/gitbucket/core/controller/ApiController.scala
index a5af352..1a64da1 100644
--- a/src/main/scala/gitbucket/core/controller/ApiController.scala
+++ b/src/main/scala/gitbucket/core/controller/ApiController.scala
@@ -13,6 +13,7 @@
     with ApiIssueCommentControllerBase
     with ApiIssueControllerBase
     with ApiIssueLabelControllerBase
+    with ApiIssueMilestoneControllerBase
     with ApiOrganizationControllerBase
     with ApiPullRequestControllerBase
     with ApiReleaseControllerBase
diff --git a/src/main/scala/gitbucket/core/controller/api/ApiIssueMilestoneControllerBase.scala b/src/main/scala/gitbucket/core/controller/api/ApiIssueMilestoneControllerBase.scala
new file mode 100644
index 0000000..5b38a58
--- /dev/null
+++ b/src/main/scala/gitbucket/core/controller/api/ApiIssueMilestoneControllerBase.scala
@@ -0,0 +1,81 @@
+package gitbucket.core.controller.api
+import gitbucket.core.api._
+import gitbucket.core.controller.ControllerBase
+import gitbucket.core.service.MilestonesService
+import gitbucket.core.util.{ReferrerAuthenticator, WritableUsersAuthenticator}
+import gitbucket.core.util.Implicits._
+import org.scalatra.NoContent
+
+trait ApiIssueMilestoneControllerBase extends ControllerBase {
+  self: MilestonesService with WritableUsersAuthenticator with ReferrerAuthenticator =>
+
+  /*
+   * i. List milestones
+   * https://docs.github.com/en/rest/reference/issues#list-milestones
+   */
+  get("/api/v3/repos/:owner/:repository/milestones")(referrersOnly { repository =>
+    val state = params.getOrElse("state", "all")
+    // TODO "sort", "direction" params should be implemented.
+    val apiMilestones = (for (milestoneWithIssue <- getMilestonesWithIssueCount(repository.owner, repository.name)
+                                .sortBy(p => p._1.milestoneId))
+      yield {
+        ApiMilestone(
+          repository.repository,
+          milestoneWithIssue._1,
+          ApiUser(context.loginAccount.get),
+          milestoneWithIssue._2,
+          milestoneWithIssue._3
+        )
+      }).reverse
+    state match {
+      case "all" => JsonFormat(apiMilestones)
+      case "open" | "closed" =>
+        JsonFormat(
+          apiMilestones.filter(p => p.state == state)
+        )
+      case _ => NotFound()
+    }
+  })
+
+  /*
+   * ii. Create a milestone
+   * https://docs.github.com/en/rest/reference/issues#create-a-milestone
+   */
+
+  /*
+   * iii. Get a milestone
+   * https://docs.github.com/en/rest/reference/issues#get-a-milestone
+   */
+  get("/api/v3/repos/:owner/:repository/milestones/:number")(referrersOnly { repository =>
+    val milestoneId = params("number").toInt // use milestoneId as number
+    getMilestonesWithIssueCount(repository.owner, repository.name)
+      .find(p => p._1.milestoneId == milestoneId) match {
+      case Some(milestoneWithIssue) =>
+        JsonFormat(
+          ApiMilestone(
+            repository.repository,
+            milestoneWithIssue._1,
+            ApiUser(context.loginAccount.get),
+            milestoneWithIssue._2,
+            milestoneWithIssue._3
+          )
+        )
+      case _ => NotFound()
+    }
+  })
+
+  /*
+   * iv.Update a milestone
+   * https://docs.github.com/en/rest/reference/issues#update-a-milestone
+   */
+
+  /*
+   * v. Delete a milestone
+   * https://docs.github.com/en/rest/reference/issues#delete-a-milestone
+   */
+  delete("/api/v3/repos/:owner/:repository/milestones/:number")(writableUsersOnly { repository =>
+    val milestoneId = params("number").toInt // use milestoneId as number
+    deleteMilestone(repository.owner, repository.name, milestoneId)
+    NoContent()
+  })
+}