The present study aimed to investigate the hiso-morphological appearance and some biochemial changes of CL in relation to its functional activity during the estrous cycle and early pregnancy in buffalo- cows. The obtained results indicated the presence of two morphologically distinct steriogenic cells. There was a relationship between the average surface area of lueal component, the fine structure of luteal cells and serum progestron at different luteal phases and at early pregnancy. Changes in LPO, NO and SOD activity, played a significant role in regulation of CL function.