Background and Aim: Sex education is an important health issue among adolescents. Mothers are the most reliable source of information for adolescents’ sex education so they should be equipped with proper knowledge, attitude, and practice to be able to educate their children properly. The present study aimed to investigate the effect of group education on knowledge, attitude and practice of mothers of adolescent girls as regards sex education in Tehran, 2015.

Materials and Methods: This was a randomized controlled trial including 30 mothers of adolescent girls randomly assigned to an intervention and 30 in a control group. The knowledge, attitude, and practice of mothers about sex education of their adolescnt girls were determined using valid and reliable researcher-made questionnaires. Based on the results, the intervention group, then, attended three educational sessions (active learning, group discussions) of 45-60 minutes duration each. The control group received only educational pamphlets. Three months after the intervention outcome variables were measured in both groups. Data were analyzed by the SPSS-22 using the Chi-Square, exact Fisher and T-tests.

Results: There were no statistically differences in the knoweldge, attitude and practice of sex education between the two groups at baseline (p>0.05). After the intervention, the mean scores of the study variables increased significantly (p<0.001) in the intervention group, while there were no statistically significant differences between the mean scores of the variables in the control group before and after the intervention (p>0.05).

Conclusion: It can be concluded that group education could bring about significant changes in the knowledge, attitude and practice of the mothers of adoloscent girls as regards sex education.