Reactive oxygen species (ROS) have various biological effects and they are non-linear in characteristic. In high oxidative stress, they may cause cytotoxicity, inhibit cell proliferation, and induce cell death in the form of apoptosis/necrosis; while in low or medium oxidative stress, ROS may cause DNA damage, cell mutation, inflammation, cell proliferation, and eventually they may induce carcinogenesis. Antioxidants are compounds with the ability to reduce ROS. Cell line MCF-7 is one of the breast cancer cell lines that is known to have small amount of antioxidant MnSOD compared to the other cell lines. Low antioxidant MnSOD level in breast cancer cell line MCF-7 leads to low concentration of hydrogen peroxide, because antioxidant MnSOD will convert radical superoxide to hydrogen peroxide. The aim of this research was to analyze oxidants and antioxidants profile in breast cancer cell line MCF-7 and their relationship with cell number. Observations were conducted for 5 days. The cell number was counted with tryphan blue method and haematometer. The concentration of radical superoxide was measured with DHE staining using LSCM tipe Olympus Fluoview FV 1000-Ver 1.7. MnSOD activity, hydrogen peroxide concentration, and catalase activity were measured with ELISA. The results showed that the longer of observation, the greater concentration of oxidants and MnSOD activity, but there was no change in catalase activity. Conclusion the increase in cancer cells number is influenced by radical superoxide.