Non-alcoholic steatohepatitis (NASH) may progress to liver cirrhosis, and NASH patients with liver cirrhosis have a risk of development of hepatocellular carcinoma. Peroxisome proliferator-activated receptor (PPAR) gamma ligand has recently been reported to have improved the condition of patients with NASH. The aim of this study was to investigate whether pioglitazone, a PPARgamma ligand, has any influence on the animal model of NASH as well as isolated hepatic stellate cells. In vivo, the effects of pioglitazone were examined using the choline-deficient L-amino acid-defined (CDAA)-diet liver fibrosis model. After two weeks, pioglitazone improved hepatic steatosis, prevented liver fibrosis, and reduced preneoplastic lesions in the liver after 10 weeks. Pioglitazone reduced the expression of TIMP-1 and TIMP-2 mRNA without changing MMP-13 mRNA expression compared to the liver fed a CDAA diet alone. In vitro, pioglitazone prevented the activation of hepatic stellate cells resulting in reducing the expression of type I procollagen, MMP-2, TIMP-1, and TIMP-2 mRNA with increased MMP-13 mRNA expression. These results indicate that pioglitazone may be one of the candidates for the benefit drugs for the liver disease of patients with NASH.