Background & Objectives: Unwanted pregnancy is a significant public health problem. One third of pregnancies occurred worldwide are unwanted. This study was conducted to assess the impact of health education based on Health Belief Model on preventive behavior of unwanted pregnancy among women in Chabahar city. Methods: For this quasi-experimental study, 94 married women aged 15-49 were selected through stratified random sampling method. Data were collected using a validated researcher made questionnaire based on Health Belief model. Reliability of the questionnaire in the aspect of knowledge, preventive behaviors, and the structure of the model were 0.87, 0.85, and 0.87, respectively. Education was delivered in two sessions through discussion and question/answer teaching methods using PowerPoint software. The differences between two groups were assessed by paired T-test, independent T-test, Pearson correlation, and chi- square tests using SPSS 19. Results: Chi-square analysis showed no significant differences in demographic information of case and control groups. Scores for knowledge, practice, and all structures of Health Belief Model in case group were increased significantly after intervention (p<0.001). Conclusion: Implemented health education program had a positive effect on knowledge, structures of Health Belief Model, and preventive behavior regarding unwanted pregnancy in case group and may play an effective role on decreasing unwanted pregnancies.