Curcumin (diferuloylmethane), the major yellow pigment isolated from the turmeric (Curcuma longa), has received much attention due to several biological properties. Curcumin exhibits a variety of pharmacological effects including antitumor, anti-inflammatory, and anti-infectious activities. In the present study, the effects of curcumin on apoptosis in the acute promyelocytic human leukemia (HL-60) cells was evaluated. Cytotoxic effects of curcumin on HL-60 cells were determined by MTT. HL-60 cells underwent apoptosis on treatment with curcumin, as indicated by increased annexin V-binding capacity and caspase-3 activation with flow cytometric analysis. Concentrations of 15, 20, and 40 μM curcumin significantly reduced cell proliferations. When HL-60 cells were treated with 10, 15, 20, and 40 μM concentration of curcumin, apoptotic rates were determined as 1.2, 81.1, 84.5, and 88.6%, respectively. On the incubations with the concentrations of curcumin, caspase-3 expressions (+) were found to be elevated by 8.5, 18.6, 91.2, and 92.4%, respectively. It was shown that curcumin had significant cytotoxic and apoptotic effects on HL-60 cells. It was suggested that curcumin may have a potential therapeutic role for human leukemia.