This study was designed to assess the effect of atrazine, the most commonly used herbicide in Egypt, on the decay process of intoxicated rat carrions and their associated forensically important insects during the summer season. Six Sprague-Dawley rats were assigned into groups. Cervical dislocation was used for killing the 1st group, and served as the control, whereas atrazine intoxication was utilized to kill the 2nd group. Control carcasses decomposed quickly, taking only 19 days to reach the skeletal stage. Decay of atrazine-intoxicated carrions was delayed since they reached the skeletal stage in 30 days. In addition, a delay in the colonization of insect fauna for atrazine-intoxicated carcasses was observed. The predominant necrophagous arthropods involved in the decomposition process were the orders Diptera and Coleoptera. The insect family Calliphoridae was the first to colonize the corpses and persisted until the beginning of the advanced decay stage. The results revealed that atrazine affected the succession pattern of carrion-feeding insects. In the control group, Dipteran insects were the most dominant insects (57.14%), and then Coleopteran insects were the following ones (42.85%). While the atrazine-intoxicated group showed 42.85% for insects of order Diptera and 57.14% for Coleoptera. This work suggested that the atrazine intoxication affected the decomposition process of rat carrions and their related arthropod fauna during the summer season, which could aid in the future forensic investigations of suspected pes- ticide poisoning