This study was conducted to find out the effect of sexual education for knowledge and attitude toward sex are elementary school students. Therefore, the present study aims to understand the changes of the knowledge are the attitude toward sex before and after the sex education, in elementary school students and then finally to provide some basic data to suggest directions for sex education. The subjects were 500 male and female elementary students from the fifth and sixth grades of 4 public elementary schools in Pusan. The subjects were assigned to a experimental (250) and a control (250) group. The research tools were sex education program and consists of physiology(menache, ejaculation), psycological(pleasure of growth), sociological(hetero sexual relationship) are about set The sex education program was given to experimental group for 6 hours by the trained school nurse's lecture using slide film and OHP film. The data were obtained before and after the sex education. Data collection was done during the period betwen Feb. 3. 1997. to Feb. 20. 1997. The collected data were analyed using frequency, percentages, $X^2$-test, means, standard deviation, t-test, ANOVA, MANCOVA with SPSS program. The results were obtained as follows : 1. The first hypotheses attained that the experimental group(19.72) is higher than the control group(12.12) on the knowledge toward sex(F=467.30, P=.000). At the physical area, the experimental group(8.84) is higher than the control group(3.96) (F=687.39, P=.000). At the psychological area the experimental group (5.18) is higher than the control group(2.63) (F=411.66, P=.000). At the social area, the experimental group (5.70) is higher than the control group (5.54), this is not significant difference (F=.67, P=.413). 2. The second hypotheses attained that the experimental group(60.42) is higher than the control group(52.48) on the attitude toward sex(F=215.70, P=.000). At the physical area, the experimental group(23.10) is higher than the control group(20.68) (F=128.68, P=.000), At the psychological area, the experimental group(20.11) is higher than the control group(16.40) (F=108.64, P=.000). At the social area, the experimental group(17.22) is higher than the control group(16.00), this is area are significant differences (F=70.37, P=.000). 3. Knowledge toward sex according to sex, religon, atmosphere of family, mother age and educational background are significant differance (P<0.05). Attitude toward sex according to sex is significant differance (P<0.05).