S-phase-kinase-associated protein 2 (SKP2) plays a crucial role in the tumorigenesis of various human cancers. Imatinib, an inhibitor of BCR-ABL tyrosine kinase, c-kit, and platelet derived growth factor receptors, has been approved for the treatment and investigation of chronic myeloid leukemia, gastrointestinal stromal tumors, and various other solid tumors. However, its efficacy in the treatment of skin squamous cell carcinoma (SSCC) has not yet been investigated. The aim of this study was to investigate whether imatinib has an antitumor effect in human SSCC cells and evaluate its functional relationship with SKP2. To research the effect of imatinib on the growth of A431 SSCC cells, we conducted a proliferation assay and flow cytometry. A western blot assay was performed to verify the function of imatinib in A431 cells and evaluate the underlying molecular mechanism. Imatinib significantly inhibited cell growth and induced cell cycle arrest at the G0/G1 phase. Furthermore, the depletion of SKP2 triggered cell cycle arrest and inhibited colony formation. Mechanistically, imatinib markedly downregulated SKP2 protein expression and subsequently upregulated P21 expression via increased protein stability. In conclusion, imatinib demonstrated an antitumor activity against SSCC cells via the SKP2-P21 signaling axis and targeting SKP2 using imatinib could be a novel therapeutic approach for SSCC that warrants further study.