Pesticides are a class of chemicals considered to kill or control pests that threaten crops, livestock, and human health. Organophosphates, cholinesterase- inhibiting pesticides, are widely used throughout the world in many different habitats. Because they are toxic to many species of pest. However, they are also toxic to many non-target species including human, and wildlife. The assessment of pesticide toxicity in mammals is crucial for understanding their potential effects on human health and the environment. Current study aimed to analyze the histopathologic and biochemical effects caused by an organophosphate pesticide, dimethoate by using in vivo mammalian model. The subchronic toxicity of dimethoate administered orally at sublethal doses to a mammalian species, Rattus norvegicus was evaluated biochemical and histopathological point of view. It is revealed that dimethoate caused differences in biochemical parameters and organ weights, and dose-related degenerative histological changes in the liver, testis and ovary of rats.