This study investigated the effect of health education on attitude towards illicit drug use among secondary school students in Diobu, Rivers State. Two (2) objectives, two (2) research questions and one (1) hypothesis guided the study. Quasi-experimental design was adopted. The researcher purposively selects the sample size of 148 students in their intact class from the population of 532 senior secondary school students from the selected senior secondary school in Diobu, Rivers State. A structured and validated instrument titled “Effect of Health Education on Knowledge of Illicit Drug Use Questionnaire” (AIDUQ) with a reliability coefficient of 0.82 was used to collect data. Descriptive statistics of frequency, percentage, mean, and standard deviation were used to answer the research questions while inferential statistics of chi-square and ANCOVA were used to test the hypotheses at a 0.05 level of significance. It was found that most of the respondent performed better in the post-test stage as there was change in attitude towards illicit drug among the students. This implies that intervention has a significant effect on the secondary school students. Subsequently, the finding showed that age do not significantly affect the effect of health education on attitude towards illicit drug use among secondary school students in Diobu, Rivers State. Based on the findings, the study concluded that health education had positive effect on secondary school students’ attitude towards illicit drug use. Finally, the study recommended among others that schools in Diobu should collaborate with drug law agencies/drug educators to conduct quarterly seminar for students on the risk of illicit drug to ensure a change in attitudes, also age were not significant in this study, further studies should be conduct on age bracket using a larger sample size and government should involve parents and community leaders in health education programs to provide a supportive environment for students and reduce peer pressure influences.