Attention, working memory and long-term memory dysfunctions are the most commonly seen cognitive impairments in schizophrenic patients. Conflicting results exist regarding the effects of antipsychotics on cognitive abnormalities. The aim of this study was to investigate the effects of atypical antipsychotic drugs olanzapine (0.4, 0.8 and 1.25 mg/kg, i.p.) and clozapine (0.5 and 1 mg/kg, i.p.) on spatial working memory in naive and MK-801 (0.2 mg/kg, i.p.) treated BALB-c mice in an 8-arm radial arm maze (RAM) task. None of the antipsychotic drugs studied altered number of errors in naive mice, whereas MK-801 significantly increased working memory errors in RAM test. Olanzapine and clozapine potently reversed MK-801 induced increasement of working memory errors. Olanzapine and clozapine prolonged latency of the animals in naive mice. The MK-801-induced enhancement in the speed of mice in performing the RAM task was blocked by olanzapine but not clozapine. Our study shows that atypical antipsychotics olanzapine and clozapine might improve cognitive deficits in schizophrenic patients.