Traditional Chinese herbal medicines are widely accepted as an option for the treatment of colorectal cancers. Danshen (Salviae miltiorrhizae Radix) is widely prescribed in traditional Chinese medicine for cardiovascular diseases. Tanshinone IIA (Tan-IIA) is extracted from Danshen. Our previous studies have shown that Tan-IIA induces apoptosis in Colo205 human colon cancer cells in vitro and in vivo. In the present study, we investigated the efficacy of Tan-IIA and 5-fluorouracil (5-FU) in a Colo205 cell xenograft model. For in vivo studies, SCID mice were engrafted with Colo205 cells and from day 10 onwards were randomly divided into 3 groups and treated with 5-FU plus Tan-IIA, 5-FU plus corn oil, and the vehicle alone. At the end of a 4-week dosing schedule, the SCID mice were sacrificed and xenograft tumors were dissected for protein western blot analysis. Our results showed that the Colo205 xenograft model co-treated with Tan-IIA plus 5-FU caused a reduction in the xenograft tumor volumes and decreased P-glycoprotein (P-gp) and microtubule-associated protein light chain 3 (LC3)-II expression compared to 5-FU alone. Based on these observations, it may be possible to develop Tan-IIA plus 5-FU as therapeutic agents for human colon cancer.