Abstract: The traditional BO medium and method using caffeine and heparin for the in vitro capacitation of bovine spermayozoa was modified in this study. Zona-free hamster eggs penetration test (HEPT) and Trypan blue-Giemsa stain technique were employed to examine the effect of mBO medium on capacitation and it was found that the new method shortened preincubation time as well as improved capacitation effect.