Repeated administration of nicotine causes incentive and behavioral sensitization in animals. Ascorbic acid administration inhibits some effects of nicotine. In the present study, the effect of ascorbic acid administration on nicotine-induced behavioral sensitization in Male Swiss-Webster mice (20-25 g) was investigated. Animals were injected with nicotine (0.25 mg/kg, i.p.) once daily for seven days in order to induce sensitization. In 9th day, an ineffective dose of nicotine (0.1 mg/kg, i.p.) was administered to the mice and the activity of the animals was recorded for 20 min in an activity monitor (30 x 30 x 20 cm). Different doses of ascorbic acid (1-1000 mg/kg, i.p.) were administered to the animals in two ways: first group; the animals received ascorbic acid at days 1-7 of the experiments 10 min before the administration of nicotine (Development). Second group, the animals received ascorbic acid only at 9th day of the experiments (Expression). The results showed that: administration of nicotine (0.25 mg/kg, i.p.) for 7 days to the mice induced behavioral sensitization in the animals. Injection of ascorbic acid (1-1000 mg/kg, i.p.) inhibits the development of nicotine-induced behavioral sensitization in the mice. Administration of ascorbic acid (1-1000 mg/kg, i.p.) was ineffective to alter the expression of behavioral sensitization induced by nicotine. In conclusion, administration of ascorbic acid may inhibit the development of nicotine-induced behavioral sensitization but is ineffective to inhibit the effects of the expression of nicotine-induced behavioral sensitization.