Objective To study bystander effect and cell death by HSV TK and ACV therapy on renal carcinoma cell lines GRC 1. Methods Different mix culture cells, which contained GRC 1/TK cells 0%、25%、50% and 100%,were treated with ACV 60 ?g/ml, the morphology and quantity of tumor cells being studied and checked with FCM and electron microscope. Results After exposure to ACV, GRC 1/TK cells, even only 25%, underwent cell death and bystander effect, but there was no obvious change in the morphology and quantity of GRC 1 cells exposed to ACV. Conclusions There were bystander effect and cell death on HSV TK and ACV therapy in renal carcinoma cell lines GRC 1. The mechanism of bystander effect may have deat with apoptosis.