The current study aimed to investigate differential expression of inhibin βA (INHβA) and inhibin βB (INHβB) in porcine oocytes before or after in vitro maturation (IVM) isolated from follicles of various sizes. Porcine oocytes isolated from large, medium and small follicles (40 from each) were used to study the INHβA and INHβB protein expression pattern using western blot analysis before or after 44 h of oocyte IVM. An increased expression of INHβA was found in oocytes collected from large and medium follicles compared with small follicles before or after IVM (P < 0.001, P < 0.05, respectively). Similarly, higher INHβB levels were observed in oocytes recovered from large follicles compared with small (P < 0.01). As INHβA and INHβB are expressed in both porcine follicular somatic cells and oocytes, it can be assumed that these transforming growth factor beta (TGFβ) superfamily factors are involved in the regulation of molecular bi-directional pathways during follicle and oocyte development, and can be recognized as markers of follicle and oocyte maturation. Moreover, the current study clearly demonstrated that inhibin expression is substantially associated with porcine follicle growth and development.