Poor development of oocytes from prepubertal animals is a major factor that hinders the application of the technology, juvenile in vitro embryo transfer (JIVET). The aim of this study was to explore the possibility of improving the developmental competence of prepubertal oocytes by supplementing the oocyte in vitro maturation (IVM) medium with antioxidants and cytokines. Effects of two antioxidants, melatonin and sericin, were first examined. The results showed that melatonin had no significant beneficial roles on the lamb oocyte development, while 0.5% sericin supplemented during IVM significantly increased the blastocyst rate of lamb oocytes (46.5% vs 19.2% in control, P < 0.05). Next, effects of two kinds of combined supplements, insulin-transferrin-selenium (ITS) and fibroblast growth factor 2(FGF2)-leukemia inhibitory factor (LIF)-insulin-like growth factor1 (IGF1)(FLI) were tested. The results indicated that addition of FLI, but not ITS, in the IVM medium, significantly improved the blastocyst development of lamb oocytes (43.9% in FLI group vs 21.6% in control, P < 0.05). Further comparison showed that the developmental competence of oocytes was not significantly different among supplementation with sericin or FLI alone or both, all of which generated similar outcomes of blastocyst yield to the supplementation with adult follicular fluid. Finally, 27 blastocysts produced from lamb oocytes matured in the presence of sericin and FLI were transferred into 18 recipients, of which 9 were pregnant. This study suggests that the developmental competence of prepubertal oocytes can be improved by supplementing IVM medium with relevant agents like sericin and cytokines.Copyright © 2020 Elsevier Inc. All rights reserved.