In this study we investigated the effect of astaxanthin (Ax), which exhibits strong antioxidant activity, during in vitro growth (IVG) on the developmental competence of oocytes and steroidogenesis of granulosa cells derived from early antral follicles. Bovine oocyte–cumulus–granulosa complexes collected from early antral follicles were cultured for 12 days in the presence or absence (control) of 500 µM Ax. The viability of oocytes and antrum formation in the granulosa cell layer during IVG culture were greater in the presence than absence of Ax (P < 0.05). Regardless of Ax treatment, 17β-oestradiol production increased during IVG culture; however, progesterone production was significantly lower in the presence than absence of Ax (P < 0.05). Reactive oxygen species levels were lower in Ax-treated oocytes than in controls after IVG (P < 0.05). Although nuclear maturation and cleavage rates did not differ