Swamp buffalo oocytes were examined to determine the specifics of early events of maturation and fertilization in vitro. A variation in germinal vesicle morphology revealed an asynchronous oocyte population at the time of collection (0 hr culture). Germinal vesicle breakdown was noticed from 8-11.7 hr of culture, Metaphase I stage at 11.7-19.3 hr, Anaphase I and Telophase I stages were seen occasionally between 19.3-21.1 hr and 21.1-22.2 hr, respectively, while Metaphase II stage was prominent between 22.2-24.0 hr of culture. The first evidence of sperm penetration was observed 1 hr after insemination. Attachment of spermatozoa in the ooplasm resulted to the initiation of 2nd meiosis and was seen from 5-8 hr post insemination. Further decondensation of penetrating sperm head in association with female chromosome decondensation, accompanied with nuclear envelope formation was noted between 8-11 hr post insemination. Opposing and apposing pronuclei were frequently seen between 22-23 hr after insemination. Syngamy, prophase stage of 1st mitotic division, including first cleavage, were observed as early as 20 hr insemination.