BP10A is a novel two-herb medicine formula, consisting of Descurainiae sophia Semen and Peucedani praeruptorum Radix. This study was done to evaluate the antitumor efficacy of BP10A and its effect on the efficacy of the anticancer drugs oxaliplatin and irinotecan (CPT-11) in a colon tumor xenograft model. Chemical constituents from the ethanol extracts of BP10A were characterized with the ultra-performance liquid chromatography (UPLC) and each constituent was quantified with the UPLC-diode array detector method. Our study showed that BP10A exerted the cytotoxic effects in two colorectal cancer cell lines and its combination treatments with oxaliplatin or CPT-11 remarkably increased the in vitro cytotoxicity of each cancer drug assessed by the Ez-cytox assay. The in vivo antitumor activity of BP10A was evaluated in three colon cancer patient-derived tumor xenograft (PDTX) models with different genetic backgrounds. Oral administration with BP10A (250 and 500 mg/kg, daily) delayed tumor growth by 34–70% in the all PDTX models. Similarly, intraperitoneal injection of oxaliplatin (6 mg/kg) or CPT-11 (20 mg/kg) also suppressed tumor growth by 31.8–60.5% or by 24.3–50.4%, respectively. Furthermore, the combination treatment of BP10A with oxaliplatin or CPT-11 remarkably enhanced the antitumor activity of each anti-cancer drug and delayed tumor growth by 47.1–74.6% or by 74.4–82.9%, respectively. In accordance with the antitumor activity, the Ki-67 expression for tumor cell proliferation and the CD31 for angiogenesis were decreased, and TUNEL staining for tumor cell apoptosis was remarkably increased by the co-treatment of BP10A and the anticancer drugs as well as by each treatment of BP10A, oxaliplatin or CPT-11. Conclusively, BP10A has a strong tumor inhibitory effect against colon cancer and a synergistic effect with anticancer drugs, suggesting that BP10A could be considered as a good therapeutic candidate for the treatment of colon cancer.