Background: Breast cancer is the most prevalent cancer and the second leading cause of cancer death in women. Because of side effects of current treatments, researchers are looking for methods with less possible side effects and highest rate of destruction of cancer cells without influencing healthy cells. Based on this, cold atmospheric plasma (CAP), is used on MCF-7 breast cancer cells. In this method, electromagnetic waves are used for destruction and death of cells. The aim of this study was to evaluate the treatment of breast cancer using CAP.
 Materials and methods: In this study, cold atmospheric plasma (CAP) with helium gas and oxygen was used for treatment of breast cancer cells (MCF-7) in different times and with using MTT assay to determine viability percentage of treated cells. Data were analyzed by one way ANOVA using SPSS software.
 Results: Viability percentage of cancer cells treated with CAP was significantly reduced compared to cancer cells not treated with plasma. Optimal treatment time of CAP for cancer cells was 45s.
 Conclusion: Cold atmospheric plasma can be considered as useful method for breast cancer cells treatment.
Keywords: Cancer, MCF-7, Cold atmospheric plasma.