Dimethoate is the widely used organophosphorous pesticide in agriculture land for controlling pests of variety of crops like citrus, cotton, tea, tobacco, fruits, olives, potatoes and vegetables. The aim of present work was to study toxic effect of pesticide dimethoate on some blood constituents and some organs of Swiss albino mice. In present investigation animals were treated with 1/10th of LD50 of dimethoate (DM) via oral gavage. The DM was administered to the animals at a dose 15mg/kg b.w. for 20 consecutive days. After completion of the dose, following hematological parameters were studied ; Hemoglobin (Hb),Red Blood Cells(RBCs), White Blood Cells (WBCs), Packed Cell Volume(PCV) and after that animals were scarified by cervical dislocation; liver and kidney dissected out and fixed for histopathological investigations. The sections were examined under light microscope. Histopathological changes observed in the liver were vacuolation, hepatic pycnosis, blood congestion, hemorrhage, nuclear death, enlargement of portal vein and high lymphatic infiltration throughout the central vein .The kidney showed some changes in cellular lining of the Bowman capsule, glomerular degereration, hemorrhage, compress blood vesslses, tubuar degeration, glomerular shrinkage ,cell rupture and hydropic changes.