The transcription of mdm2 gene is activated by p53 and this limits the growth‐suppressing activity of p53 by direct binding. It has been reported that MDM2 protein is overexpressed in several types of cancers. However, there have been no immunohistochemical studies on MDM2 in human hepatocellular carcinoma (HCC). We immunohistochemically examined the expression of MDM2 and the relationships between its expression and histological grade, clinicopathological parameters, p53 expression and patient survival in 107 patients with HCC. The frequency of MDM2 positivity in the nuclei of HCC cells was 28/107 (26%). There was no correlation between the MDM2 expression and HCC grade. However, positivity of MDM2 expression significantly correlated with small HCC size (p<0.05, χ² test) and the absence of vascular invasion (p<0.01, χ² test). No significant differences were noted between MDM2 expression and capsular invasion or satellite nodules. Expression of MDM2 showed a significantly positive correlation with expression of p53 (p<0.03, χ² test). Patients with positive expression of MDM2 had poorer prognosis than patients with negative MDM2 expression. MDM2 expression was the most useful independent factor for overall survival (p=0.0001). MDM2 was expressed in 26% of HCC, and its expression correlated positively with p53 mutations. MDM2 over‐expression is a useful predictor of poor prognosis in patients with HCC following hepatic resection.