Let-7 microRNA is expressed in lower lever in a variety of human tumors and is involved in tumorigenesis. This study investigated the inhibitory effect of the let-7g microRNA on the expression of the HMGA2 gene in the fluorouracil (5-Fu)-resistant human hepatoma cell line Bel-7402/5-Fu, and the effect of let-7 g microRNA on drug sensitization in Bel-7402/5-Fu cells. Let-7 g microRNA and negative microRNA plasmids were constructed and transient transfected into Bel-7402/5-Fu cells. Expression levels of HMGA2 mRNA and protein in microRNA transient transfectants were clearly reduced as compared with negative microRNA transfectants and untreated cells. Flow cytometry revealed increased in S phase in let-7 g microRNA cells. dimethylthiazol-diphenyltetrazolium bromide (MTT) results indicated that microRNA transfectants had a higher cell inhibition rate than the negative vector or untreated cells after treatment with 0.13-13 microg/ml 5-Fu. In addition, cyclin A was down-regulated in the let-7 g transfectants cells.The results showed that let-7 g microRNA contributed to an increase of 5-Fu-induced cell cycle inhibit in human hepatoma cell and sensitized cells to 5-Fu, leading to increased the effectiveness of the drug in treating hepatoma cancer.