Chlorpyrifos is commonly used pesticide for crop protection against pests and also in various public health operations. In the present study, the ability of chlorpyrifos to induce apoptosis and the influence of oxidative stress in induction of apoptosis was investigated; using avian lymphocytes model (white leghorn) in-vitro. Lymphocytes were treated with 10 –5 M for 24 and 48 h. MTT assay revealed decreased viability in time dependent way. Fragmentation assay showed DNA ladder upon agarose gel electrophoresis. Annexin V binding assay detected the phosphatidylserine exposure to outer leaflet of the plasma membrane. Electron microscopy showed margination of chromatin, membrane blebbing, which are the features of apoptosis. Western blot analysis revealed the expression of HSP 60, and other small molecular weight proteins, indicative of oxidative stress. The above results suggest, chlorpyrifos have the potential to induce apoptosis and the oxidative stress might mediate the apoptotic death in chlorpyrifos-treated lymphocytes. Thus the study advocates the systematic use of chlorpyrifos when used for various public health operations.