Although genetic basis of childhood temperament has been well documented in western populations, little is known about whether genes play an important role in childhood temperament in East Asians. The present study examined mother's ratings of Emotionality, Activity, and Sociability (EAS) in 894 pairs of 2- to 9-year-old South Korean twins. The best-fitting model indicated that 34 to 47% of the variances of the EAS were attributable to genetic factors, with the remaining variances being due to the effects of environmental experiences unique to each child. Common family environmental factors were negligible. Genetic variances for Activity and Sociability were primarily nonadditive, whereas those for Emotionality were additive. In spite of well known cultural differences in child rearing practices, social values, and the mean levels of temperament between East Asian and western populations, the pattern of additive vs. nonadditive gene actions and heritability estimates found in the present sample were remarkably similar to those reported in western twin samples. There were no significant age or sex differences in genetic or environmental influences. Overall, these results corroborate cross cultural generality of genetic influences on childhood temperament.