Objective;To investigate the repressing effects of cytosine deaminase(CD) and herpes simplex virusthymidine kinase(HSVtk) double suicide genes coexpression system on human cholangiocarcinoma QBC939 cells and QBC939 cells transplantated tumor in nude mice. Methods;CD and HSVtk double suicide genes were transfered into QBC939 cells using liposomes. After G418 selection, the positive clones of QBC939/CD+tk cells were picked up and cultured. The expression of CD and HSVtk genes was confirmedby RTPCR. In vitro, the QBC939/CD+tk cells were treated with 5Fc and/or GCV, and the cytoxicity efficacy was evaluated by microculture tetrajolium test (MTT) method. The QBC939/CD+tk cells were inoculated subcutaneously into nude mice, and when the tumors were palpable, 5Fc and GCV were injectedintraperitoneally, and the volumes of transplantated tumors were measured before and after medication. Results;Double suicide genes were stably expressed in QBC939/CD+tk cells. The repressing capability of combination of 5Fc and GCV on QBC939/CD+tk cells was more effective than that of using either 5Fc or GCV alone. The increase of cellrepressing was assaciated with increase the concentration of the prodrug. The repressing effect of combination of the 2 prodrugs on early period of transplantation tumor was obvious, even complete abolition of tumor was noted, and moreover a marked local bystander effect was observed. Conclusions;In vitro and in vivo, the cellrepressing efficacy of double suicide gene system on cholongiocarcinoma cells and the tramsplanted tumor of nude mice was significant, and the bystander effect was obvious.