Cisplatin is one of the most effective chemotherapeutic agents and plays a major role in the treatment of a variety of human solid tumors. However, its toxicity limits the clinical use. Recently, the administration of antioxidants has been suggested to protect against cisplatin-induced nephrotoxicity. The present study was designed to estimate the antitumor activity of the licorice extract alone and in combination with cisplatin, and its protective potential against cisplatin-induced toxicity in a mouse xenograft model. The administration of the licorice extract significantly inhibited tumor growth in BALB/C mice inoculated with CT-26 colon cancer cells. The combination of the licorice extract and cisplatin diminished the therapeutic efficacy of cisplatin but promoted considerably antitumor activity of the licorice extract. In mice with cisplatin treatment for 15 d, the serum levels of blood urea nitrogen and creatinine remarkably were increased by kidney damage, and the serum alanine aminotransferase and aspartate aminotransferase levels were elevated by liver damage. The administration of the licorice extract plus cisplatin recovered these functional indices in the kidney and liver to almost the control levels. In addition, the administration of the licorice extract significantly reduced the cisplatin-induced oxidative stress. Taken together, the administration of the licorice extract inhibits the growth of mouse colon carcinoma without any adverse effects, and reduces the cisplatin-induced toxicity. Therefore, the licorice extract may be a candidate for an anticancer and chemopreventive agent. However, cancer patients with cisplatin therapy should avoid the supplementation of the licorice extract.