Objectives: To analyze the weekly variations of birth by using by analyzing the birth certificated data of Korea Statistics. Methods: The analysis was based on birth data of Korea (715,020 births in 1995, 493,471 births in 2003, 470,171 births in 2010 and 484,550 births in 2012). For analyzing of weekly variation in birth, we used the average number of births per day of the week and the index of birth occurrence (IBO). IBO is defined as a ratio of the average number of births per day of the week to the average number of births per day of the year. Results: The daily average of birth was significantly lower at weekends and national holidays than on weekdays, they have become more concentrated on weekdays during 1995-2012. The variations of daily average of birth for 2012 (coefficient of variation: 21.2) showed wide fluctuation as compared with daily average of birth for 1995 (17.9). There was a range of 11 to 17 percent decrease in birth on weekends and holidays, and 6 percent increase on Monday during the periods. The most popular day of week to give birth continue to be Monday, Tuesday and Friday during 1995-2012. Index of birth occurrence in 2012 was highest for Monday (114), and lowest for Sunday (59) followed by holidays (62) and Saturday (78). Conclusions: There was a significant variation in weekly day of birth in Korea.