diff --git a/internal/api/handler.go b/internal/api/handler.go
index af720a7..3200b26 100644
--- a/internal/api/handler.go
+++ b/internal/api/handler.go
@@ -260,6 +260,26 @@ func (h *Handler) StartPaperIngest(c *gin.Context) {
 	c.JSON(http.StatusAccepted, job)
 }
 
+func (h *Handler) ReindexPaper(c *gin.Context) {
+	id := strings.TrimSpace(c.Param("id"))
+	if id == "" {
+		writeError(c, http.StatusBadRequest, errors.New("id is required"))
+		return
+	}
+
+	optCtx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
+	defer cancel()
+
+	if err := h.ingest.ReindexPaper(optCtx, id); err != nil {
+		writeError(c, http.StatusInternalServerError, err)
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{
+		"paper_id": id,
+		"status":   "reindexed",
+	})
+}
+
 func (h *Handler) GetTask(c *gin.Context) {
 	id := c.Param("id")
 
diff --git a/internal/api/router.go b/internal/api/router.go
index a34f6cb..f4d43e8 100644
--- a/internal/api/router.go
+++ b/internal/api/router.go
@@ -49,7 +49,7 @@ func NewRouter(opts RouterOptions) http.Handler {
 			papers.GET("/:id/download", h.DownloadPaper)
 			papers.GET("/:id/chunks", h.ListPaperChunks)
 			papers.POST("/:id/ingest", h.StartPaperIngest)
-			papers.POST("/:id/reindex")
+			papers.POST("/:id/reindex", h.ReindexPaper)
 		}
 
 		tasks := v1.Group("/tasks")
diff --git a/internal/ingest/service.go b/internal/ingest/service.go
index 4aaf71b..9fd8150 100644
--- a/internal/ingest/service.go
+++ b/internal/ingest/service.go
@@ -250,3 +250,35 @@ func parsedMarkdown(paper domain.Paper, doc docparser.Document) string {
 
 	return b.String()
 }
+
+func (s *Service) ReindexPaper(ctx context.Context, paperID string) error {
+	if s.search == nil {
+		return fmt.Errorf("search backend is not initialized")
+	}
+
+	paperID = strings.TrimSpace(paperID)
+	if paperID == "" {
+		return fmt.Errorf("paperID cannot be empty")
+	}
+
+	// get chunks
+	chunks, err := s.chunks.ListByPaperID(ctx, paperID)
+	if err != nil {
+		return fmt.Errorf("get chunks by paperID: %w", err)
+	}
+
+	if len(chunks) == 0 {
+		return fmt.Errorf("paper %s has no chunks", paperID)
+	}
+
+	// delete first, update next
+	if err := s.search.DeleteByPaperID(ctx, paperID); err != nil {
+		return fmt.Errorf("delete chunks by paperID: %w", err)
+	}
+
+	if err := s.search.IndexChunks(ctx, chunks); err != nil {
+		return fmt.Errorf("replace chunks by paperID: %w", err)
+	}
+
+	return nil
+}