Experiments were conducted to determine the effects of beta-mercaptoethanol ($eta$-ME) supplements to the in vitro maturation (IVM) medium on in vitro fertilization (IVF) and intracellular glutathione (GSH) concentration. Porcine cumulus-intact oocytes were matured in TCM-I99 medium containing porcine follicular fluid, sodium pyruvate, D-glucose, FBS, hormonal supplements, and $eta$-ME (0, 25, 50 and 100 ${mu}$M) for 36 to 46h. After culture, cumulus-free matured oocytes were co-incubated with epididymal spermatozoa for 18h. There were no significant differences in the maturation rate among treatment groups. However, increases (P < 0.05) in intracellular GSH concentration before and after. fertilization were observed in 50 ${mu}$M $eta$-ME supplements to the IVM medium. Also, increases (P < 0.05) in male pronuclear formation after IVF were observed in same treatment group. In conclusion, supplementing $eta$-ME into the IVM medium increased intracellular GSH concentrations and increased fertilization in vitro.