The objective of the present work was to study the effect of a nonsteroidal aromatase inhibitor (fadrozole) on proliferation, estradiol production, aromatase expression and telomerase activity in pig granulosa cells from small and large follicles. The cells were treated with fadrozole for 48 h and 72 h in basal and FSH-stimulated conditions. Fadrozole caused a decrease of H-3-thymidine incorporation in granulosa cells derived from small and large follicles. The proliferative potential of small-follicle GC was significantly higher under all culture conditions. Estradiol production was suppressed both granulosa cell populations cultured in the presence of fadrozole for 48 and 72 h. Fadrozole caused a decrease of aromatase gene expression in small-follicle granulosa cell incubated for 72 h and in large-follicle GC after 48 h of culture.