Pain is a general symptom of many diseases. The medicinal plant Viola odarata (V.O.) has a particular position as an analgesic in traditional medicine. In this study, the analgesic effect of aqueous extract of this plant was studied. The extract was prepared using suxhlet method. The extract was than concentrated. Then, the extract was dissolved in normal saline to produce the desired concentrations. The analgesic effect was evaluated using formalin test in male mice. The average weight of mice was 25 g. In this test, formalin 5% (s.c.) was used. The extract and ASA was injected i.p. ASA was injected at a dose of 300 mg/kg and extract was administered at doses of 10, 50, 100, and 200 mg/kg. The results indicated that extract at a dose of 100 mg/kg had maximum analgesic effect (P<0.01) and the extract at this dose was more effective in attenuation of chronic pain as compared to ASA (P<0.05). Meanwhile, it was ineffective in acute phase of formalin test.