The interaction of electromagnetic fields (EMF) with living organisms presents an increasing source of interest nowadays. There are reports on the influence of EMFs on memory. In this study, the effect of a 50 Hz, 50G EMF was investigated on passive avoidance learning in male rats. For this purpose, male Wistar rats (n = 50, 6-8 weeks, 250-300 g) were randomly divided into five groups. Control group trained in passive avoidance box and tested 24 hours later. Other groups exposed to EMF immediately after training for 1, 4, 6 and 8 hours respectively, and 24 hours later were tested. Data obtained show that increasing the time of exposure to EMF from 1 hour to 4 hours causes a significant reduction in retention latency (P<0.05) as compare to control group. It is concluded that EMF can disturb memory consolidation, but this disturbance is closely related to exposure time.