A series of novel imidazolone derivatives were designed and synthesized via a rational drug design strategy. These compounds were obtained from 3-substituted imidazolidine-2,4-dione through alkylation, formylation, dehydration, and amination. The structures were characterized by (1)H NMR, (13)C NMR, and MS. All target compounds were screened for their DPP-4 inhibitory activity in vitro. The results revealed that some imidazolone derivatives showed potent DPP-4 inhibition. Compound 5b had an IC50 value of 2.21 µM inhibitory activity against DPP-4. As a promising lead compound, compound 5b with DPP-4 binding mode was further studied by docking analysis. The expected interaction mode was obtained.