The objective of this study was to determine the new bioactive compounds through gas chromatog.-mass spectrometry anal. and the cytotoxic activity of two rodent tuber mutant plants against breast cancer cells. Further, the cytotoxicity activity of rodent tuber mutant plants was tested on breast cancer cell line performed by 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazolium bromide assay method. Results: This results study confirmed that the presence of phytochem. composition in the tuber of rodent tuber mutant plants KB 6-1-3-4 and KB 6-9-5 was found six bioactive compounds from fatty acid groups which have the potential as an anticancer compound, such as octadecanoic acid, hexadecanoic acid, hexadecanoic acid Me ester, 9-octadecanoic acid, linolelaidic acid Me ester, and butanoic acid. The results showed that extracts from rodent tuber mutant plants had a cytotoxicity effect on MCF-7 cancer cells with half maximal inhibitory concentration (IC50) values that were lower than the control (mother plant). In vitro tests of KB 6-1-3-4 and KB 6-9-5 against MCF-7 cancer cell lines have IC50 values of 12.482μg/mL and 7.043μg/mL, resp., while it had a lower cytotoxicity effect with the IC50 value of control plant was 19.113μg/mL. The mutant plants of KB 6-9-5 have 3 times more effective than control. Conclusion: The results of this study clearly indicated that rodent tuber mutant plants have shown promising as an anticancer drug on breast cancer.