Argininosuccinate synthetase (ASS) has previously been proven to be reductively expressed in hepatocellular carcinoma (HCC) and various types of HCC cell lines. Arginine, the product of ASS, has been used as a target in HCC by recombinant human arginase or arginine deiminase, which is now in the phase II clinical trial stage. This study aimed to present the levels of ASS expression in HCCs and its correlation with clinicopathological features and prognosis of HCC patients. Immunohistochemical detection of ASS was performed on samples from 71 patients with HCC. Positive staining was found in 21 HCCs, with a score of 2, as well as in normal liver tissues. Reduced ASS staining was found in 70.4% (50/71) of HCC tissues, including 21 with a score of 0 and 29 with a score of 1. The staining score in cancer tissues was significantly associated with gender, background liver, histopathological differentiation, recurrence, TNM staging and portal vein invasion (P<0.05), but not with age, viral status, tumor size and serum α-fetoprotein level. Patients with a high ASS expression had significantly poorer overall and disease-free survival (P<0.001 and P<0.001, respectively). These data showed that ASS was reductively or negatively expressed in a large portion of HCC, and that ASS levels in HCCs correlated inversely with prognosis. In conclusion, a high expression of ASS may be a novel marker of poor prognosis of patients presenting with HCC.