This study was done on 81 rats to evaluate the post mortem interval PMI depending on expression of Gapdh mRNA and protein response to immunostaining. Gapdh in liver demonstrated less stability &degradation with a significant decrease in amplicon detection across the entire transcript after 48 hour PMI with no difference in transcript level until 96 hours, and showed a strong significant positive correlation between PMI and Gapdh expression (r = 0.837, p = 0.000). Consistent and surprising robustness of Gapdh transcript levels in brain with non-significant low correlation between gene expression and PMI (r = 0.129, p = 0.522). Gapdh showed less stability with significant decreases in transcript levels in liver with increasing PMI (up to 48 hour). However, it shows low correlation between Gapdh transcript and PMI in brain. PCNA showed positive immunostaining in the hepatocytes cytoplasm and in the nuclei in the first few hours after death (0-9hours), later on only few cells showed positive immunostaing in both cytoplasm and nuclei (12hours). At 24-48 hours the hepatocytes only showed positive cytoplasmic PCNA reaction, while in 72-96 hours the PCNA immunostaining showed negative reaction. In the brain at 0-12 hours, positive PCNA was located in the cytoplasm and nuclei of the nerve cells. At 24 hours only positive PCNA immunostaining was located in the cytoplasm and negative reaction in the nuclei. At 48-96 negative PCNA immunostaining was noticed.