We detected a strong upregulation of the mutated transketolase transcript (TKTL1) in human hepatoma cell line HepG2, whereas transketolase (TKT) and transketolase-like-2 (TKTL2) transcripts were not upregulated. We inhibited the expression of TKTL1 by RNAi in HepG2 cells. It was found that total transketolase activity was dramatically downregulated and the proliferation of cancer cells was significantly inhibited in HepG2 cells. These results indicate that TKTL1 gene influences total transketolase activity and cell proliferation in human hepatoma cells, suggesting that TKTL1 gene plays an important role on glycometabolism in tumors and it might become a novel target for tumor gene therapy.