In the present work we investigated the effects of brown rice extracts on proliferation and apoptosis of cancer cells. Brown rice extracts were prepared using nongerminated brown rice versus germinated brown rices. Mouse leukemia L1210 cells, human acute lymphoblastic leukemia Molt4 cells, and human cervical cancer HeLa cells were treated with either nongerminated brown rice extract (N ex), water-germinated extract (W ex), chitosan-germinated extract (C ex), glutamic acid-germinated brown rice extract (G ex), or chitosan/glutamic acid-germinated brown rice extract (CG ex). The concentrations of gamma-aminobutyric acid (GABA) in the G ex and CG ex were three and 3.3 times higher than the GABA concentration in the N ex, respectively. The G ex and CG ex retarded significantly the proliferation rates of L1210 and Molt4 cells, and the highest retardation rate was with CG ex. In addition, the G ex and CG ex enhanced significantly apoptosis of the cultured L1210 cells, but no significant apoptosis was seen with the other extracts, which have lower concentrations of GABA than G ex and CG ex. These results show that brown rice extracts with enhanced levels of GABA have an inhibitory action on leukemia cell proliferation and have a stimulatory action on the cancer cell apoptosis.