Abstract: The present investigation on the modulatory effects of zinc on NMDA receptors in this study the effects of intra dorsal (CA1) hippocampus injection of NMDA receptor agonist and antagonist to passive avoidance task in the presence and absence of ZnCl2 have been investigated in adult male rats, by using step down apparatus. So, 10 groups (n = 8) rats were considered, first group as a control, the second group received 0.1 μg rat-1 NMDA in 0.5 μL saline for 4 days immediately after shock. Third group receives 1 μg rat-1 MK-801 in 0.5 μL saline 10 min before training for 4 days. Sham groups receive saline at the same condition. Five remain groups received 100 mg/kg/day ZnCl2 in drinking water for 2 weeks. Sixth group only receives 100 mg/kg/day ZnCl2, but other groups (7, 8, 9 and 10), in addition of consumption ZnCl2, receive drug or saline in the same condition to 2, 3, 4, 5 groups. While administration of NMDA improve the impairment effects on ZnCl2 consumption (p<0.05), present results showed that consumption of 100 mg/kg/day ZnCl2 on adult male rat`s impair both learning and memory (p<0.05) but administration of MK-801 increasing the impairment effects of ZnCl2 (p<0.05). It seems that consumption of zinc chloride influence on passive avoidance learning and memory by its effects on NMDA receptor subunits in the hippocampus.