Breast cancer was the second most common cancer that causes death in women worldwide. One ingredients of herbal plants as an alternative therapy in the community, was gambir leaves. This research was conducted to examine the anticancer activity of Uncaria gambir Roxb on T47D breast cancer cells in vitro. Six levels of concentration U. gambir (31.25 mg/ml up to 1000 mg/ml) was included on the 96 microplate well which had been filled with breast cancer cells, the positive control was doxorubicin (with concentration of 0.03-1 mg/ml). The anticancer effects of U. gambir was determined by MTT (3-[4, 5-dimethylthiazol-2-yl]-diphenyl tetrazolium bromide 2.5). The results showed the existence of anticancer activity of Uncaria gambir Roxb at concentrations of 250, 500 and 1000 μg/ml. The largest anticancer activity found at a concentration of 500 μg/ml with the percentage of apoptotic cells of breast cancer by 20%, but we also found a decrease in the value of the apoptotic at concentration of 1000 μg/ml. The IC50 of U. gambir was 1.086 μg/ml whereas the IC50 doxorubicin was 0.108 μg/ml. This study concluded that the inhibition of breast cancer cell growth by gambir leaves extract was still quite weak compared to doxorubicin.