Human Mob as tumor suppressor 1 (MATS1) has been shown to play a crucial role in tumor growth by regulating cell proliferation and apoptosis. We evaluated the expression of MATS1 in colorectal cancer patients and assessed its clinicopathological significance. MATS1 mRNA expression in paired tumor/normal samples from 72 cases of colorectal cancer was evaluated, using real-time RT-PCR analysis. MATS1 protein expression was determined by immunohistochemical staining. MATS1 mRNA expression was significantly lower in tumor tissues than in normal colorectal tissues (p<0.05). Clinicopathologically, factors such as incidence of large tumor size, deep invasion, lymphatic permeation and liver metastasis were significantly more frequent in the low MATS1 expression group (p<0.05). Prognosis of the low expression group tended to be poorer than that of the high expression group. MATS1 protein expression was diminished in tumor cells compared with corresponding non-cancer colon epithelial cells. MATS1 mRNA expression is suppressed in tumor tissue and its low expression is associated with tumor growth, invasion and metastasis of colorectal cancer. Specifically, low MATS1 expression may be a good marker of liver metastasis, a life-threatening indicator for colorectal cancer patients.