Dipeptidyl peptidase?4?(DPP4) has been revealed to be upregulated in women suffering from polycystic ovary syndrome (PCOS), which is a common reproductive disorder. The present study was designed to investigate the effects of inhibition of DPP4 expression on the proliferation of ovarian granulosa cells as well as on the activation of the cAMP response element?binding protein?(CREB)/aromatase pathway. The expression levels of DPP4 in rat serum samples with or without PCOS and ovarian granulosa cells (KGN cells) were detected using reverse transcription?quantitative PCR (RT?qPCR) and western blot analyses. Cell viability and cell cycle progression were detected using the Cell Counting Kit?8 assay and flow cytometric analysis, respectively. The 5?ethynyl?2'?deoxyuridine assay was employed to detect the proliferation of glycolaldehyde?bovine serum albumin (GOA?BSA)?treated KGN cells. In addition, RT?qPCR and western blot analyses were applied to detect the expression levels of CREB, specific cell cycle?associated proteins and cytochrome P450 (CYP)?19A1 and CYP11A1 enzymes in KGN cells. The expression levels of DPP4 were upregulated in rats with PCOS. Inhibition of DPP4 expression promoted the proliferation and cell cycle arrest of KGN cells. It was also revealed that the expression levels of cell cycle?associated proteins were upregulated in DPP4?silenced KGN cells. In addition, their proliferation was decreased following treatment with GOA?BSA, while the addition of sitagliptin partially reversed these effects. Additionally, sitagliptin reversed the inhibitory effects caused by GOA?BSA treatment on the cell cycle progression and on the activation of the CREB/aromatase pathway in KGN cells, as determined by the increased expression levels of the cell cycle?associated proteins as well as those of the CREB protein and the CYP19A1 and CYP11A1 enzymes. In conclusion, inhibition of DPP4 expression promoted the proliferation of KGN cells and the activation of the CREB/aromatase pathway.