This study investigated the activation of oocytes after microinjection of sperm extracts (SE) from miniature pig spermatozoa. SE was prepared from miniature pig sperm by sonication for 35 min and centrifugation 100,000 g for 1 h. Injection of SE 0.3 mg/ml into porcine oocytes produced the highest activation rate (41.8%). SE injection into bovine oocytes induced similar activation (43.3%). The porcine oocyte activation rate (63.4%) was significantly (p<0.05) improved when SE was purified with a 2-D clean-up kit. When SE was heat treated at 60°C for 30 min, it failed in activation. However, SE succeeded in activation when stored at 4°C for 48 h or was freeze-thawed 5 times using liquid nitrogen. The activation rates were 42.1% and 31.4%, respectively. The results indicate that SE from miniature pig sperm might have an oocyte activation factor, and that the factor might have stability at low temperatures, though it appears to be inactivated at high temperatures.