Potential of Rhodomyrtus tomentosa as a native anticoagulant been tested by evaluating the possible haemostatic effect of Rhodomyrtus tomentosa aqueous leaf extract in vitro. In vitro coagulation assays such as Thrombin time (TT), Prothrombin time (PT) and Activated partial thromboplastin time (APTT) tests were performed on normal coagulation control plasma spiked with different concentrations of the leaf extract (10 – 100%). Total tannin and flavonoid for all different concentrations of leaf extract was measured using spectrophotometer. The results were analyzed using one way ANOVA followed by post-hoc Dunnet’s and Pearson’s correlation. The results showed that TT, PT and APTT of normal coagulation control plasma spiked with extract were markedly prolonged. A significant anticoagulant (p < 0.05) showed by PT was at lowest concentration (10%), TT was at concentration 50 – 100% and APTT was at concentration 80% - 100%. The clotting times for TT, PT and APTT were significantly correlated (p < 0.05) with total tannin and flavonoid. In summary, a potent anticoagulant effect of Rhodomyrtus tomentosa significantly higher in extrinsic pathway (PT) and the bioactive compound of tannin and flavonoid attributes to the anticoagulant activity of Rhodomyrtus tomentosa.