Abstract: Objective To investigate the inhibitory effect of small interfering RNA on the expression of CD147 and invasion in human thyroid carcinoma cell line K1.And to screen the effective siRNA sequence. Methods Three pairs sequence of CD147-siRNA small interfering RNA designed and synthesized and were transfected into K1 cells to knockdown the CD147 expression.The mRNA and protein levels of CD147 were detected by RT-PCR and ELISA.The mRNA and protein levels of MMP7 were detected by RT-PCR and Western blot.Transwell chambers were used to detect the invasiveness ability of K1 cells in vitro. Results Compared with the normal group and control group,mRNA and protein level of CD147 in S1 group had no significant difference(P>0.05).In contrast,mRNA and protein level of CD147 decreased significantly(P<0.05) in the S2 and S3 groups,in which mRNA level decreased to 67.81% and 72.48%, respectively;and protein level decreased to 31.65% and 35.47%,respectively.Meanwhile,compared with the normal group and control group,mRNA and protein level of MMP7 in the S2 and S3 groups also decreased significantly，in which mRNA level decreased to 50.25% and 53.40%, respectively,and protein level decreased to 41.58% and 40.49%,respectively.In transwell chamber assay,after transfection 72 h,the invasion inhibition rate of the cells went through membrane in the S2 and S3 groups was 35.87% and 30.16%,respectively,which was less than thatin the S1 group.While there were no significant difference(P>0.05) among the S1,normal and control groups in the results from Transwell assay mentioned above. Conclusion CD147-siRNA in the S2 and S3 groups can decrease the expression of CD147，resulting in the suppression of invasiveness activity of tumor in vitro.The use of CD147 specific siRNA deserves further investigation as a novel approach to cancer therapy in the future.