Abstract Background: Sexually transmitted diseases are a major health problem that affects mostly young people. The aim of the study was to assess the effect of providing educational sessions about sexually transmitted diseases on knowledge and attitudes of secondary school students. Methods: A quasi-experimental research design was used in carrying out the study. The study was conducted at four governmental public secondary schools in Zagazig City, 367 secondary school students from the previously mentioned settings were included in the study. Two tools were used to collect necessary data: Tool (I): An interview questionnaire; It which consisted of two parts: Part (A) entailed questions pertaining to socio demographic characteristics of the students, while part (B) included questions regarding student’s knowledge about sexually transmitted diseases. Tool (II): It was intended to assess student’s attitudes toward sexually transmitted diseases. Results: Pre, post and follow up students’ knowledge and attitudes tests after sessions' implementation revealed highly statistically significant improvements in students’ knowledge and attitudes (p < .001), which justified the research hypothesis. Conclusion: The educational sessions significantly brought out improvements in the knowledge and attitudes of adolescent students regarding sexually transmitted diseases. The study recommended health educational sessions about STDs should be provided to all students in the schools with illustrated booklets for maintaining knowledge of its most important types. Furthermore, media enlightenment campaigns about these diseases should also be emphasized. Key Words: Secondary School Adolescents, Educational Sessions, Knowledge, Attitudes Sexually Transmitted Diseases.