The objective of this study was to analyze the trend of sex ratio at birth from the vital statistics of National Statistical Offices during 15 years(1980∼1994). The total of registered birth during the period were 10,770,756 cases. The trend of sex ratio at birth increased from 103.9 in 1980 to 115.4 in 1994. Seasonality of sex ratio was higher in January and lower in March. The variation between yearly mean sex ratio and calendar month sex ratio showed a slight decline from 1980 to 1994. The regression analysis showed a statistically significant liner trend : Sex ratio = 103.39 + 0.064(time) + 4.808(january) + ......... + 0.790(November); (R2 = 0.615, P<0.001). The sex ratio was estimated to be 116.9 in 1995 and 120.86 in 2000, according to the equation. In Korea in recent years, male live births bave exceeded those of females by amounts far greater than those that occur naturally in human population. This imbalance of sex ratio may plausibly be attributed to sex selective abortion and other factors; decreasing early mortality rate, higher proportion of first birth order in total births, shorther period between marriage and first birth, and lower total fertility rate.