Cysteamine has been reported to disturb learning performance in rats. Our study was made to determine if this is also true in mice. Adult male ddY mice were subjected to a battery of learning tests following our standard experimental protocols. Cysteamine injected 30 min prior to the learning trial dose-dependently increased the number of errors in the testing trial of step-down test, and its effect was statistically significant at a dose of 200 mg/kg. In the lever press test, 200 mg/kg injection of cysteamine also suppressed the conditioned avoidance rate. However, no significant changes were observed in other tests. These results suggest that the learning disorder induced by cysteamine in mice is restricted to a specific type of behavioral performance. In conclusion, the mechanism by which cysteamine generates learning deficiency in mice may differ from that in rats.