Estimation of the postmortem interval (PMI) is a very essential task for forensic experts, especially in criminal cases. The PMI is the time passed since the death of an individual and refers to the stages of autolysis. The current study was designed to estimate PMI by determination of the oxidative markers, RNA integrity, GAPDH mRNA level in the brain of adult male albino rats and the autolytic ultrastructure changes of the cerebrum at time of death (0 hour), and then on 1st, 2nd, 4th, and 6th hours postmortem (hpm). Thirty-five male albino Wistar rats were included in the present study (Seven rats for each time). The results revealed a significant timedependent malondialdehyde elevation with a decrease the antioxidant CAT, SOD, and GSH started from the 1st till the 6th hpm. On the other hand, the brain tissue GAPDH-mRNA gene expression level showed a significant decrease at the 1st and the 6th hpm. The ultrastructure changes showed significant autolytic changes in the nerve cell, the nerve axon, and the blood vessels starting from the 1st till the 6th hpm. In conclusion, oxidative markers and ultrastructure examination of the brain tissue especially cerebrum could be helpful for determination the early postmortem interval time.