Summary The role of activin-A in follicular development and on the mRNA expression levels of different genes in goat secondary follicles was evaluated. Goat secondary follicles (≥150 μm) were cultured for 18 days under control conditions or with the addition of either 50 or 100 ng/ml activin-A (Experiment 1). The mRNA levels for the genes that code for activin-A, ActR-IA, ActR-IB, ActR-IIA, ActR-IIB, follicle stimulating hormone receptor (FSH-R) and P450 aromatase were measured in each condition (Experiment 2). We observed that after 6 days of culture, the antrum formation rate was higher in cultures with added activin-A than in the cultured control (P < 0.05). The addition of 50 ng/ml activin-A increased the follicular growth rate in the final third of the culture (days 12-18), resulting in a higher percentage of meiosis resumption (P < 0.05). On day 6, the addition of activin-A (50 ng/ml) increased the levels of ActR-IA mRNA compared with the cultured control (P < 0.05). After 18 days, the addition of 50 ng/ml activin-A significantly increased the levels of its own mRNA compared with the non-cultured control. Moreover, this treatment reduced the mRNA levels of P450 aromatase in comparison with the cultured control (P < 0.05). Higher levels of P450 aromatase mRNA were found for both activin-A treatments compared with the non-cultured control (P < 0.05). No difference in estradiol levels was detected among any of the tested treatments. In conclusion, the addition of activin-A to culture medium stimulated early antrum formation as well as an increase in the daily follicular growth rate and the percentage of meiosis resumption.