Breast cancer is the most commonly diagnosed invasive malignancy and first leading cause of cancer-related deaths in Iranian women. Based on silymarin's unique characteristics, its application in chemotherapy combined with doxorubicin can be effective to enhance the efficacy together with a reduced toxicity on normal tissues. The present study focus on evaluate the efficacy of silymarin in combination with doxorubicin, on viability and apoptosis of estrogen-dependent breast carcinoma cell line (MCF-7). After being cultured, MCF-7 cells were divided into 8 groups and treated as follows: 1st group received 75 μg silymarin, groups 2, 3, and 4 were treated with 10, 25, and 50 nM doxorubicin, respectively, and groups 5, 6, and 7 respectively received 10, 25, and 50 nM doxorubicin as well as 75 μg silymarin. Viability percentage and apoptosis of the cells were assessed with Trypan Blue staining after 16, 24, and 48 hours. Silymarin has a synergistic effect on the therapeutic potential of doxorubicin. Use of silymarin in combination with doxorubicin can be more effective on the therapeutic potential of doxorubicin and decreases its dose-limiting side effects.