During ovarian follicular growth and development, only a few follicles actually ovulate. Recently, it was found that follicular atresia is triggered by granulosa cell apoptosis, but the molecular mechanism of follicular atresia was not understood. Using flow cytometry, we found that miR-34a promotes granulosa cell apoptosis in pig ovarian follicles. In addition, inhibin beta B was found to be a miR-34a target gene, based on luciferase reporter assays, quantitative RT-PCR and Western blotting. Taken together, our data indicate that miR-34a plays an important role in granulosa cell apoptosis by targeting the INHBB gene in the porcine ovary.