Background and purpose: Embryos produced from in vitro assisted reproductive technologies (ART) manipulations, such as parthenogenesis, are less developmentally competent than in vivo-derived embryos. This study was designed to evaluate the effect of L-carnitine treatment during IVM on maturation of immature oocytes selected by Brilliant Cresyl Blue (BCB) staining, and their subsequent developmental competence after parthenogenesis. Materials and methods: Immature oocytes collected from NMRI mice ovaries were stained with BCB for 90 min. BCB+ oocytes (with blue color cytoplasm) were then cultured in tissue culture medium (TCM) 199 with 0.0, 0.3 and 0.6 mg/ml L-carnitine at 37 °C and 5% CO2 under maximum humidity. After 24 hours, nuclear maturation (using Hoechst staining) and cytoplasmic maturation (by measuring the intracellular glutathione (GSH) concentration with monochlorobimane) were recorded in metaphase II oocytes. Cleavage rate, blastocyst development rates (BDR) and total cell number of blastocyst were also determined after parthenogenesis. Results: Both L-carnitine concentrations significantly increased GSH (P<0.01), nuclear maturation (P<0.01) and BDR (P<0.05) compared with those in the control group. L-carnitine had no significant effect on cleavage rate and total blastocyst cell numbers. Conclusion: These results demonstrated that L-carnitine supplementation during IVM of immature BCB+ oocytes could increase developmental competence of oocytes after parthenogenesis, possibly by improvement of nuclear and cytoplasmic maturation of oocytes.