This study investigated the feasibility of using an hammerhead ribozyme against C Ⅱ TA, a major regulator of MHC Ⅱ antigens, to repress the expression of MHC Ⅱ molecules on Hela cells. A hammerhead ribozyme (Rz464) specific to 463-465 GUC triplet of C Ⅱ TA and its target gene were transcribed, then mixed up and incubated in vitro. The cleavage products were analyzed by PAGE and silver-staining. Rz464 was then inserted into the pIRES2-EGFP vector (pRz464). Stable transfectants of Hela with pRz464 were tested for class Ⅱ MHC induction by recombinant human interferon-gamma (IFN-γ). mRNA of C Ⅱ TA was measured by RT-PCR. Our results showed that Rz464 could exclusively cleave C Ⅱ TA RNA. When induced with IFN-γ, the expression of HLA-DR, -DP, -DQ on pRz464+ Hela was induced, and the mRNA content of C ⅡTA decreased too. It is concluded that Rz464 could inhibit C Ⅱ TA and thus the family of genes was regulated by C Ⅱ TA:MHC Ⅱ molecules. These results provided insight into the future application of Rz464 as a new nucleic acid drug against auto-immune diseases.