This study aimed to investigate the residual activity ofganophosphorus insecticides in cow’s farm under normal conditions ofeding and spraying program . Its objective was determination ofganophosphorus insecticide residues in animal feed (green fodder andncentrated mixture) and, in turn , their build up in milk as an endroduct. Samples were collected during winter and summer seasons 1993-94. This study , on the other hand, was initiated to elucidate the effectDiazinon as one of the most common used organophosphorussecticides in veterinary field on serum cholinesterase and serum calciumcattle after spraying with the recommended dose of the drug (0.01 %) .’I) : Organophosphorus Insecticide Residues in Animal Feed.The results of this experiment showed that the orgnophosphorushsecticides detected in green fodder were Diazinon , Methamidophs,alathion , Pirimiphos-methyl and Chlorpyrifos. The first 3 compoundsere detected in both winter and summer seasons with mean values of.0022 , 0.0013 and 0.0191 ppm at winter season and 0.0024,0.0071 and.0402 ppm at summer season, respectively. Pirimiphos-methyl andhlorpyrifos were detected in summer only with mean values of 0.0002d 0.0013 ppm , respectively.Concerning to concentrated mixture , the results showed theresence of organophosphorus residues in winter as well as summer. Theean values of organophosphorus insecticide residues detected in the