Histone deacetylases (HDACs) play an important role in chromatin remodeling, gene repression and regulating cell cycle progression and differentiation. This study was designed to clarify the role of HDAC1 expression in hepatocellular carcinoma (HCC). The expression of HDAC1 in 47 patients with surgically resected HCC was immunohistochemically examined and analyzed in relation to their clinicopathological factors. The patients were divided into two groups according to the expression status of HDAC1: a high HDAC1 group (n= 25) with more than 20% of positively stained cells and a low HDAC1 group (n= 22) with 20% or fewer positively stained cells. A high HDAC1 expression indicated a higher incidence of cancer cell invasion into the portal vein, a poorer histological differentiation, and a more advanced TNM stage. The survival rates after a surgical resection in low and high HDAC1 patients at 1, 3, 5 and 10 years were 100, 95.5, 81.8 and 60.8% and 88.0, 60.0, 40.0 and 32.0%, respectively (p= 0.008). A multivariate analysis using the Cox regression analysis showed that a high HDAC1 expression was an independent prognostic factor of HCC in patients after hepatic resection (relative risk: 10.1, p= 0.0018). High HDAC1 expression might have an important role in the aggressiveness and cell dedifferentiation, and its expression status may be a useful biomarker for predicting the outcome of the patients with HCC.