Introduction & Objective: Early diagnosis of breast cancer plays a key role in decreasing the number of deaths. Knowledge about the symptoms of breast cancer is a good way for its early diagnosis. Materials & Methods: This descriptive study was conducted on 400 females who attended Alzahra Hospital. A questionnaire consisting of three parts was used; 13 questions related to demographic information, 16 questions for assessing their knowledge, and 4 questions for their practice. The validity and reliability of questionnaire were confirmed. Data were analyzed with SPSS 16 and for comparison the t-test, ANOVA and Pearson correlation coefficient, were used. Results: The mean age was 48.07±6.44 and the mean score of the knowledge was 5.2±3.0. 57.2% of individuals had low knowledge and only 4.5 percent had high knowledge. Doing self-examination and mammography as practice, was 43.8 and 23.25 respectively. There was a direct correlation between age and knowledge score (P = 0.017). Knowledge score of women who did self breast examinations and those took mammography was significantly higher than other groups (P = 0.05). The married patients had higher knowledge score (P = 0.04). There was no relation between their level of literacy, job, financial condition, number of pregnancies, number of children, and history miscarriages or breast and ovary cancers in her or her family, with score of knowledge. Conclusions: Knowledge and practice of women about breast cancer was very low. Therefore, it is suggested to increase the knowledge of people in order to prevent late diagnosis.