Drugs and alcohol concentrations are regularly used as evidence in criminal and civil litigations. The interpretation may be critical to the thorough investigations of different types of forensic cases whether antemortem or postmortem. So, the aim of the present work is to study the effect of putrefaction on the postmortem detection of ethanol and diazepam. The study was conducted on 96 adult male albino rats divided randomly to four groups 24 rats for each and every group is further subdivided into 4 subgroups (a, b, c, and d) 6 animals for each subgroup. Group I: control group received 1ml distilled water. Group II: rats received lethal dose of ethanol. Group III: rats received lethal dose of diazepam. Group IV: rats received lethal dose of both ethanol and diazepam. After death of treated animals, control animals were sacrificed at the same time and immediate dissection of subgroup a was done. Rats of subgroups b ,c and d were dissected after death at 18 hours, 24 hours and 48 hours respectively. The livers were extracted for detection of ethanol and diazepam. The control group showed increased liver ethanol in subgroups I-c and I-d. Liver ethanol of group II and IV showed gradual elevation by increasing post mortem interval while there was no considerable change in liver diazepam of group III. As regards liver tissue diazepam of group IV, a non-significant elevation was detected in the subgroups IV-b, IV-c and IV-d as compared to the subgroup IV-a.