Objective To investigate the antitumor effects of triptolide against CT26 colon cancer and its impact on the expression of Polo-like kinase-1 (PLK-1) protein.  Methods  Forty clean grade BALB/c mice, each mouse was implanted with 1×10⁶ CT26 cells into the dorsal side of the right forelimb to establish a tumor-bearing mouse model. Experimental animals were randomly divided into four groups, the tumor model group (saline control), the positive drug group ［oxaliplatin, 5mg/(kg·d)］, the low-dose triptolide group ［50μg/(kg·/d)］, and the high-dose triptolide group ［100μg/(kg·d)］. The drugs were administered through intraperitoneal injection (10 times in total, once every other day). The in vitro effects of the drugs on the proliferation, migration, invasion, and mitosis of CT26 cells were also assessed.   Results  Triptolide significantly inhibited the proliferation, migration, and invasion of CT26 colon cancer cells, and disrupted the separation of centrosomes and the correct arrangement of chromosomes during the prophase of mitosis in tumor cells. The binding energy of triptolide and PLK-1 protein was -7.1 kcal/mol, and it could down-regulate the expression of PLK-1 in CT26 cells.  Conclusion  Triptolide exerts its antitumor effects against CT26 colon cancer by downregulating the expression of PLK-1.