Three sexually mature and clinically normal buffalo bulls were used in this experiment to study the effect of injectable selenium (Se) on quality. and freezability of Egyptian buffalo semen and on plasma testosterone concentration. The bulls were almost at the same age (3.5 years) and body weight (550 kg) at the beginning of the experiment. The data were collected throughout a 12 weeks period. This time interval comprised a pro-treatment period of four weeks (control) and a supplementary period of 8 weeks. During the supplementary period. each bull was injected intramuscularly with 10 mg Se twice weekly. The semen was collected by means of artificial vagina twice weekly. Twenty four ejaculates collected during pro-treatment period and 4B ejaculates collected during Se supplementation period were extended in Tris—egg yolk-glycerol extender and packed into mini straws (0.25 ml). After 4 h equilibration at 5°C. these straws were frozen in vapour of LN; and stored for 24 h at ~196°C before thawing and evaluation. The supplementary 86 significantly (P < 0.05) increased ejaculate volume (2.8 vs. 2.06 ml). live sperm (69.6 vs. 61.3%). sperm concentration (1.41 vs. 1.03 x 10°iml) and sperm output (4.0 vs. 2.11 x 10") per ejaculate and significantly (P < 0.05) decreased sperm abnormalities (10.4 vs. 15.0%) as compared to the pro—treatment period. In addition. treatment with injectable Se increased fructose and Se concentrations in semen. Also, supplementary Se significantly (P < 0.05) increased blood serum testosterone (0.695 vs. 0.26 ngfml). The treatment with So resulted in higher (P < 0.05) frozen-thawed motility and live spermatozoa compared to the pro-treatment period. It is concluded that injection of 10 mg Se twice weekly should be considered adequate for improvement of quality and freezability of Egyptian buffalo semen.