Spermatogonial stem cells (SSCs) serve as the foundation of spermatogenesis and play a critical role in livestock fertility and genetic improvement. However, maintaining these cells in long-term culture remains challenging, especially in pigs, where preserving both proliferative capacity and the undifferentiated state has proven difficult. To overcome this limitation, we investigated SB216763 (SB), a selective GSK-3β inhibitor reported to enhance proliferation in other stem cell types, for its potential effects on porcine spermatogonial cells (pSCs). In a 9-day concentration screening (0, 1.25, 2.5, and 5 μM SB), SB treatment significantly enhanced the proliferation of pSCs. It upregulated the proliferation-related gene PCNA and the antiapoptotic gene BCL2, while downregulating key apoptosis-related genes, including BAX and Caspase-3. It also promoted the expression of DAZL, UCHL1, NANOS2, and OCT4. Furthermore, over a 55-day period, treatment with 2.5 μM SB consistently supported higher proliferation rates, a larger proportion of DAZL-positive cells, and elevated expression of undifferentiation-associated markers (NANOS2, OCT4) compared with untreated controls at each passage. Overall, our results demonstrate that SB216763 not only promotes the proliferation of pSCs but also helps maintain their germline identity, offering a feasible strategy to improve the long-term in vitro culture of porcine spermatogonial cells.