Objective: study aims to examine the effect of acetaminophen in male rats after early postnatal exposure to acetaminophen, on several behavioral outcomes and its role to precipitate the autistic like behavior with investigating the ameliorating role of melatonin on these parameters. Materials and Methods: Thirty healthy Albino male rat pups were selected for this study. At post natal day 3 (PND3), rat pups were divided into three groups (10 pups group). Group1were served as a control group were injected SC with NS for 7 days then gavaged with NS for 2 weeks , Group 2 pups which were injected SCin a dose (50 mg/kg) of acetaminophen once daily for 7 days then these pups were gavaged with NS for 2 weeks. Group 3 : pups which were injected SC in a dose (50 mg/kg) acetaminophen once daily for 7 days then gavaged with melatonin (10 mg/kg) for 2 weeks. behavioral test, such as nest seeking test at PND 9, the negative geotaxis test was done at "PND 15 and 17", open field test at PND21 Results: acetaminophen exposed pups exhibited a significantly difference in behavioral tests: nest seeking test showed that the time of pups of acetaminophen group to approach maternal bedding was (10.00±1.51) sec which was significantly higher than time of control group. At PND15, NG test showed a significant increase in time spend to rotate 180° of the pups of acetaminophen group when compared with that of the control group and melatonin group. While at PND17, showed a significant increase in time spend to rotate 180° in NG test of pups of the acetaminophen group when compared with that of the control group and that of the melatonin treated group. open field test showed that pups of acetaminophen group were traveled significantly number of squares crossed (31±8.34) compared to those traveled by pups of control and melatonin treated groups (22±7.43).. Conclusion: Administration of acetaminophen from PND 3 to PND10 induces autistic like behavioral manifested by several alteration in rat pups. These alteration were ameliorated by administration with melatonin (10 mg/kg for 2 weeks) after exposure to acetaminophen.