Introduction & Objective: Breast cancer is one of the most common cancers in women throughout the world including Iran. There are currently more than 40000 women in Iran suffering from the disease. Studies have shown that the active form of vitamin D, increases cell differentiation and inhibits proliferation, can play a role in changing the risk of breast cancer. Materials & Methods: Present study is analytical and case-control study. In this study150 women with breast cancer and150 women without breast cancer as control were investigated. Including criteria was diagnosis of breast cancer in all cases and absence breast cancer in all control group. Serum vitamin D level, age and marital data included in check list. The obtained data were subjected to chi square, logistic regression and two samples t-test by SPSS software version 23. In all analyses P ˂ 0.05 were as significant difference. Results: Mean level of serum vitamin D in case and control groups were 16.73 ± 11.95 and‌ 27.04 ± 18.49 ng/ml, respectively (‌P < 0.001). Based on multivariable analysis of logistic regression, the risk of developing breast cancer increased with a decrease in serum vitamin D levels. At the level of vitamin deficiency (10 > ng/ml), the odds ratio of illness were 1.93 times higher than the inadequate level. (%95 CI: 0.281; 0.954, P = 0.035), and the odds ratio of getting the disease were 6.9 times higher than the adequate level of vitamin D (%95 CI: 0.075; 0.361, ‌P < 0.001). Also, the serum vitamin D level with estrogen receptors and progesterone receptors was significantly correlated‌ (P‌ < 0.001), but there was no significant correlation with HER-2 receptor ‌(P = 0.195). Conclusions: Based on this study, patients with breast cancer had significantly lower levels of serum vitamin D in comparison with healthy women. Therefore, decreases in serum vitamin D levels are associated with an increased risk of breast cancer.