Abstract: Methidathion is a non-systemic organophosphorus insecticide. Genotoxicity potential of methidathion was evaluated in rat bone marrow cells (in vivo) using different doses based on LD50 by means of micronucleus test. MNNCE (Micronucleated Normocromatic Erythrocytes) and MNPCE (Micronucleated Polychromatic Erythrocytes), NDI (Nuclear Division Index) and NDCI (Nuclear Division Cytotoxicity Index), necrotic and apoptotic cells were recorded in rat’s bone marrow samples.