Background: FDY003 is a traditional Korean medicine that has been developed as a complementary therapy for cancer. FDY003 contains various herbs such as Lonicera japonica, Artemisia capillaris Thunb., and Cordyceps militaris known to exhibit antioxidant and anticancer activities. Objective: The objective of this is to determine whether FDY003 represents a complementary therapy for colon cancer when it is injected using a syringe. Materials and Methods: High-performance liquid chromatography (HPLC) analysis was performed to determine the active ingredients of FDY003. The effect of FDY003 on the proliferation of Colo205 cells was investigated using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay. The antioxidant effects of FDY003 on Colo205 cells were ascertained using oxidative markers such as lipid peroxidation and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Markers of apoptosis in Colo205 cells after treatment with FDY003 were also measured. Based on the in vitro results, in vivo experiments were performed using Colo205 cell-induced xenograft mouse cancer model treated with FDY003. Results: HPLC analysis revealed that FDY003 contained various active ingredients known to possess antioxidant activities. The viability of Colo205 cells was decreased by FDY003 in a concentration-dependent manner. Cancer size and weight were significantly decreased in the group treated with FDY003, similar to those in the group treated with anticancer drug irinotecan. The expression of Bcl-2-associated X protein and caspase-3 was increased in cancer tissues derived from the FDY003-treated group. Serum levels of lipid peroxidation and DPPH were also significantly increased in the FDY003-treated group. Conclusion: FDY003 represents a potential complementary therapy for cancer due to its antioxidative effects and anticancer activity.