The aims of the present study were to: (a) examine the expression of IL‐18 signalling receptors in TCs across different stages of bovine antral follicle development; (b) use non‐luteinized bovine TC culture models to investigate whether IL‐18 affects steroid production; (c) explore the potential biological effects of IL‐18 on TCs proliferation in follicles sampled; (d) detect the effect of IL‐18 on the key enzymes in steroid hormone synthesis of TCs; (e) determine whether the effect of IL‐18 can be attenuated by IL‐18BP; and (f) explore the possible roles of IL‐18 in the pathogenesis of PCOS. This evidence concerns the gene IL18 and polycystic ovary syndrome.