Objective: Horizontal centrifugation was believed may improve platelet, leukocyte, and growth factors in the buffy coat. Previous study of platelet concentrates metronidazole incorporation was able to greatly inhibit bacteria. Metronidazole might help the proliferation with its ability to inhibit pro-inflammatory cytokines. This study intended to examine the influence of C-PRF and i-PRF with and without metronidazole incorporation horizontal pre-centrifugation towards periodontal ligament fibroblast proliferation. Material and Methods: 2x104 fibroblast cells on the 96 well plates were added with 1 ml of each buffy coat platelet concentrates. The samples were split into five groups: i-PRF, C-PRF, i-PRF metronidazole, C-PRF metronidazole, and control group. Then monitored after 1 day, 3 days, and 5 days using MTT assays. The data were inspected by Two Way ANOVA Test and Post Hoc Test. Results: The result indicated that cell proliferation of fibroblasts was escalated by the addition of C-PRF, i-PRF metronidazole incorporation, and C-PRF metronidazole incorporation group. While the i-PRF group showed decreasing proliferation cell count. Conclusion: This study assumed that platelet concentrates (i-PRF and C-PRF) with metronidazole incorporation can increase the cell proliferation higher than i-PRF and C-PRF only.