This study was conducted to investigate the effect of cysteine (CySH) and glutathione (GSH) on in vitro maturation of porcine follicular oocytes. The results obtained were summarized as follows: 1. When the immature oocytes were cultured at 0, 0.04, 0.14, 0.6 and 1.2 mM of cysteine (CySH) for 36h, the germinal vesicle breakdown (GVBD) rates were 90.8, 89.9, 90.5, 92.0 and 91.3%, respectively, and the maturation rates of the oocytes with metaphase-II were 56.1, 50.7, 41.9, 49.0 and 61.5%, respectively. Especially, the maturation rates of 0.14 and 0.6 mM treated groups were significantly lower than those of control (non-treated) group (P<0.05). After 44h of culture in the same treatments of CySH, the GVBD rates of porcine immature oocytes were 90.0, 91.8, 89.8, 90.5 and 89.6%, respectively, and the maturation rates were 80.2, 76.3, 69.4, 66.7 and 72.6%, respectively. Especially, the maturation rates of 0.14 and 0.6 mM treated groups were significantly lower than those of control group (P<0.05). 2. When the immature oocytes were cultured at 0, 0.05, 0.1, 0.5 and 1.0 mM of glutathione (GSH) for 36h, the GVBD rates of porcine immature oocytes were 91.0, 90.9, 89.5, 92.0 and 91.1%, respectively, and the maturation rates were 59.0, 48.5, 47.8, 38.6 and 37.5%, respectively. All treated groups of GSH showed lower maturation rates than the control group (P<0.05). After 44h of culture in the same treatments of GSH, the GVBD rates of porcine immature oocytes were 91.8, 94.1, 89.1, 91.3 and 91.1%, respectively, and the maturation rates were 84.6, 57.1, 69.6, 71.3 and 64.3% respectively. All treated groups of GSH showed lower maturation rates than the control group (P<0.05).