A total of 1,974 married couples were investigated for natural conception rate and the time required to become pregnant after cessation of contraceptive measure. Among them, 33 couples were infertile due to various causes and 52 couples employed contraceptive method continuously. Therefore, the time intervals of natural conception were available for analysis only in 1,889 couples. Fourteen hundred and sixty-seven women (77.6%) became pregnant within 3 months after exposure to the risk of conception, 1,683 (89.0%) within 6 months, 1,793 (94.8%) within one year and 1,855 (98.0%) within 2 years. The correlations among conceptive probability, history of using contraceptive methods, age of marriage, and menstrual status were discussed.