Women live much longer than men in Korea, with remarkable gains in life expectancy at birth for the past decades. The gender differential has steadily increased over time, reaching a peak of more than 8 years in 1980s, and decreased thereafter to 6.7 years in 2005. Studies to investigate the pattern and contributing factors to changes in the life expectancy gender gap have been mostly from Western countries, and there has been no such study in Asian countries, except in Japan. We therefore aimed to examine age- and cause-specific contributions to the changing gender differentials in life expectancy in Korea, in particular the decline of the gap, using a decomposition method. Between 1970 and 1979 when the gender gap in life expectancy widened, faster mortality decline among women in ages 20-44 explained 66% of the total increase in the gender gap, which would be due to substantial improvements in reproductive health among women and excess male mortality in occupational injuries and transport accidents. Although greater survival advantage among elderly women over 70 contributed to further increase in the gender gap, the contributions from younger ages with the ages 15-64 contributing the most (-2 years) resulted in the overall reduction of the gender gap which began in 1992 and continued to 2005. Among causes of death, liver diseases (-0.5 years, 38% of the total decline), transport accidents (-0.4 years, 31%), hypertensive diseases (-0.3 years, 19%), stroke (-0.1 years, 11%), and tuberculosis (-0.1 years) contributed the most to the overall 1.4 years reduction in the gender gap. However, changes in mortality from lung cancer (+0.3 years), suicide (+0.3 years), chronic lower respiratory diseases (+0.2 years), and ischemic heart diseases (+0.1 years) contributed to widening the gap during the same period. In sum, while smoking-related causes of death have contributed most to the narrowing gap in most other industrialized countries, these causes contributed toward increasing the gender gap in Korea. Instead, liver disease, hypertension-related diseases, and transport accidents were major contributing causes of death to the narrowing of gender differentials in life expectancy in Korea.