Introduction: Breast cancer is one of the most prevalent types of cancer in women, and its incidence is on the increase. Knowledge and practice of breast self-examination are important strategies for early detection of the disease. The general objective of this study was to determine the effectiveness of health education on breast self-examination amongst secondary school girls in Anambra State, Nigeria. Methodology: It was a before and after interventional study with control, in which 261 school girls were selected by multi-stage sampling method. The study group (197) which received health education was assessed contemporaneously with the control (64) at the pre- and post-intervention stages. Data was collected via self-administered questionnaire. Before health education, questionnaires were administered to assess their baseline knowledge, attitude and practice of breast self-examination. The study group received information on breast self- examination, but the control group had health talk on the basics of hand washing technique. Questionnaires were administered again to both groups to assess the effectiveness of education on breast self-examination. Data was analyzed and presented in tables. Result: Showed a significant increase in the percentage score for knowledge from 40.9% to 85% for the study group as opposed to the control group which percentage score remained unchanged at 47.1%. The attitude scores of respondents in both groups which were almost the same before education (93.4% and 87.5% respectively) before education, did not record significant changes following education (98% and 84.4% respectively).Overall the practice score reduced markedly from 67% to 39.6% among study group (p