Cancer is a malignant tumor with characteristics of uncontrolled cell growth, poor metastasis, leading to the dysfunction of organs and death of patients. Many efforts have been made, including the exploration of natural products. The purpose of this study was to determine the cytotoxicity of the Dillenia suffruticosa leaf extract against the cell lines MCF-7 and HepG2. The method used is an experimental research design with a completely randomized design. The treatment group consisted of the leaf extract of 500, 1,000, 2,000, 5,000, and 9,000 ppm for the brine shrimp lethality test (BSLT). The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) test used 10, 15, 20, 25, and 50 ppm concentrations and control (without extract). The data on the BSLT test was determined by analyzing the lethal concentration 50 (LC 50 ) value using the probit analysis, while the MTT test was determined by analyzing the IC 50 and analysis of variance test. The BSLT test results showed an LC 50 value of 5,221 ppm, which means that the leaf extract is not toxic. Simpor leaf extract at 25 ppm with IC50 of 88.52 was seen as the best concentration for liver cancer treatment. It can be concluded that D. suffruticosa shows cytotoxicity against the cell lines MCF-7 and HepG2 and can be used as a candidate for breast and liver cancer treatment.