Five sexually mature buffalo-bulls with poor semen quality, were injected intramuscularly with selenium. Each animal received 90 mg of selenium as sodium selenite. divided into 3 doses with one week interval in-between. Semen samples were collected weekly from Se-treated bulls during the period of experiment (12 weeks) and from the controls. The enzymatic constituents of the seminal plasma (GOT, ACP, AKP and LDH) after injection were significantly increased in parallel with the improvement of the physical characters of the semen. The significant variations in lipidogram (total lipids, cholesterol and plasma free fatty acids) in seminal of low fertile bulls were restored after Se-injection, to be nearly similar with the results of fertile bulls.