In Turkey, there is neither systematic nor structured child sexual abuse prevention programs for school-aged children in school settings. The main purpose of this study was to investigate the effectiveness of a school-based child sexual abuse prevention program on elementary school (4th grade) students. Quasi-experimental design with pretest, post-test and control group was used. The subjects consisted of 36 fourth grade students; 18 randomly assigned to the experimental and 18 randomly to the control group. For the experimental group, a 'preventing child sexual abuse psycho-educational training program' as an independent variable was carried out by the researchers. The topics were about personal rights, 'my body belongs to me', good touch-bad touch discrimination, breaking promise, body safety rules, say "No", and bad secrets, talking with a grown up who believes the child, sexual abuse is never a child's fault, etc. One hour session, with a ten minute break, were carried out on four consecutive days. During this period, the control group did not receive any treatment. ANCOVA analysis showed the students who attended the sexual abuse prevention program scored significantly higher than the control group (p<05). The effect size of the study was calculated by Cohen's d, and it was .80 which is satisfactory. As a result, the prevention child sexual abuse program was effective on 4th grade students and this effect was lasting eight weeks later. This study was the first experimental effort to prevent children from child sexual abuse in the school context in Turkey.