This study aimed to investigate the mechanism of circ-POLA2 in colon cancer (CC). Circ-POLA2, miR-138-5p, and SEMA4C levels in CC tissues and cells were recorded. The influences mediated by circ-POLA2, miR-138-5p or SEMA4C on cell proliferation, migration, invasion, and apoptosis were determined. The feedback loop of circ-POLA2/miR-138-5p/SEMA4C was surveyed. As measured, circ-POLA2 and SEMA4C were highly expressed, while miR-138-5p was poorly expressed. Meanwhile, circ-POLA2 could mediate SEMA4C through miR-138-5p targeting. Circ-POLA2 knockdown caused the blockade for cell activities, but this effect was alleviated by miR-138-5p inhibition or SEMA4C overexpression. Overall, circ-POLA2 is tumorigenic for CC through miR-138-5p/SEMA4C axis, which may provide a promising molecular target for CC therapy.