Purpose: This study was done to identify sexual maturity, sexual knowledge and sexual attitude in late elementary school children and to provide basic data to develop more concrete and practical applications for sexual education. Method: The participants were 1,959 fifth and sixth graders from 8 elementary schools in Busan and Gyungnam. Result: Sexual maturity for boys was at the $1.3{pm};.6$ stage and pubic hair $1.2{pm};.6$. Breast maturity for girls was at the $2.3{pm};.7$ stage, and pubic hair, $1.7{pm};.8$. Of the boys, 5.9% had experienced nocturnal emission, and of the girls, 20.9% had experienced menarche. Sexual knowledge was lower than the mean. They were not well informed about contraception and sexual disease. Sexual knowledge of girls and of sixth graders was higher than boys and fifth graders. The more mature students had higher sexual knowledge. Sexual attitude was generally positive but was more positive for girls than for boys. Sexual maturity, sexual knowledge, and sexual attitude were positively correlated. Conclusion: Because sexual maturity comes earlier, systematic sexual education is needed for elementary students. Institutional and economic support should continue to be given to the sexual education programs in school, home and community.