Background: Onset of menstruation is one of the most important changes occurring during adolescence. The aim of this study was to evaluate the effect of health education program on menstrual practices among secondary school girls. Subjects and Method: A quasi-experimental research design was used in carrying out this study. The study was conducted in four governmental public secondary schools for girls in Damietta city. One hundred and thirty three female students fulfilled the study criteria were included in the study. A  structured interviewing Questionnaire sheet and hygienic facilitiesobservational checklist' for secondary schools were utilized as tools for collecting data. Post-test was done after 3 months to assess the impact of the program. Results showed that more than two-thirds of the studied students in the pre test reported having symptoms of RTI, in the post test, these symptoms slightly decreased but the difference observed wasn't statistically significant. Most  of the students had healthy  practice score level regarding  all aspects related to menstrual hygiene in the post-test compared to the pre-test. The majority of them abstained  from performing normal activities in the pre test. Meanwhile, In the post test, highly statistical significant differences were seen with regard to the previous items, where (P-value = 0.001). There was highly statistical significant difference between studied students' total practice score levels and their social class. Conclusion & recommendations: The educational program was successful in attaining its aim of positively changing practices and behaviors of  the studied students regarding menstruation. School health nurse should provide loud and clear messages on menstrual hygiene for adolescent girls and their mothers which can be achieved through parent meetings and group discussion based on scientific facts, considering physical, social and mental changes of adolescent girls. Secondary school students need to be supported with clean school environment supplied with clean bathrooms  in addition to other basic hygienic products to help them manage their hygiene.