Background: Sexual harassment is a form of sexual violence and recently, it has become a global social problem that threatens the future of childhood. Aim of the study: was to evaluate the effect of preventive program on mother’s knowledge regarding child’s sexual harassment. Subjects and Methods: Research Design: A quasi experimental design was utilized in this study. Setting: The study was conducted in pediatric hospital, Zagazig university hospitals at cardiopulmonary department, nutrition department and dialysis department. Subjects: The study was conducted on sample of 93 mothers who attended the previous setting and had a child aged 6-12 years and agreed to participate in the study. Tools of data collection: Two tools were used for collection of data, the first tool was a structed interview Questionnaire for mothers’ characteristics, their children and mothers’ background regarding sexual harassment in children. The second tool was a structured knowledge questionnaire to assess the mothers’ knowledge regarding prevention of child sexual harassment. Results: The studied mothers mean age was 34.78 ± 5.52 years. 51.6% of studied mothers had three children and 38.7% of mother’s children aged from 6-8< years with a mean age 9.04± 2.02 years. 50.5% of studied mothers and 48.4% of fathers had university education. 47.3% of the studied mothers experienced sexual harassment with different forms while 11.8% of their children were sexually harassed. 3.2% of the studied mothers had satisfactory knowledge pre-intervention compared to 95.7% post-intervention. Conclusion: It can be concluded that the mother’s knowledge regarding sexual harassment prevention had been improved significantly after implementation of the program. Recommendations: Continuous educational programs for all parents regarding sexual harassment and how to protect their children as well as sexual harassment educational guidance must be provided for all children to improve their knowledge about sexual harassment.