This study analyzes the structural characteristics of rapid changes in Korean population, using the data of a census and other data on the changes in the population. Major findings are : 1. During 1950~1955, annual increase rate of population was about 1.02%, about 2.88% during 1955~1960, and 1.36% during 1980~1985. It is expected to decrease to 0.07% during 2015~2020. 2. Major Age Composition 0~14 is expected to reduce to 16.5% in 2020 from 41.2% in 1955, while the ratio of population aged 15~64 is expected to increase to 72.1% from 55.5%. Furthermore, for the population group of age 65 and over is expected to increase from a mere 3.3% to 11.4%. 3. The aging index of population is expected to increase to 69.5 in 2020 from 8.0 in 1955 and so the old dependency ratio is expected to 15.9 from 6.0 4. The median age is expected to 40.2 in 2020 from 19.0 in 1955. 5. In 2020 the child-woman ratio is expected to reduce to 22.3 from 64.7 in 1955. 6. In 2020 the age index of 0~4 is expected to 57.4 from 169.4 in 1955, and the age index of 65~69 to 261.7 from 95.6 on the contrary.