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Background and Objective: The majority of medicines are associated with some form of side effects due to high prevalence of self- medication in Iran .There is not any drug without side effects the prevalence of self- medication in Iran's provinces is increasing. This study was done to determine the knowledge and practice among woman about self -medication based on health belief model. Materials and Methods: This cross- sectional study carried out on 385 women whom referred to health centers in Isfahan, Iran during 2008. Data were collected by a questionnaire including knowledge, practice and health belief model structures. Results: The mean score of knowledge was 82.97±13.80 and means score of perceived susceptibility 72.48±17.11, severity 71.60±14.73, benefits 68.29±17.13 and barriers 61.64±19.67. 86% of women have done self–medication at least in one disease in 6 months earlier Including: cold 225 (57.6%), headache 28 (53.7%) and anemia 51 (13.2%). The main reasons for self –medication were previous experience and medicine accessibility .The main reasons to avoid self –medication was the side effects of medicine. Conclusion: Self-medication can be prevented thought increasing knowledge and education about severity of drug side effects.