The objective of study was to investigate the relationship between expressions of CIITA and MHC molecules in five human cell lines. The expressions of MHC molecules and CIITA protein were detected by Western blot, immunohistochemistry and flow cytometry. The expression of CIITA gene was measured by RT-PCR. The results indicated that the expression of MHC-II molecules in 5 human cell lines was consistent with expression of CIITA. The cell lines constitutively expressed CIITA also expressed MHC-II molecules, the expression of MHC-II molecules in cell lines expressed CIITA after induction with IFN-gamma also recovered; the cell lines unexpressed CIITA after induction with IFN-gamma did not respond to IFN-gamma-promoting expression of MHC-II molecules. It is concluded that some cell lines cannot express MHC-II molecules which may be related with deficiency of CIITA expression. It suggest that CIITA participates in regulation of MHC-II molecule expression, which may plays a certain role in escape from carcinogenesis under surveillance of immune system.