OBJECTIVE To investigate the effect and mechanism of modified Lichong decoction （MLCD） on the apoptosis of transplanted tumor cells in nude mice. METHODS Human gastric cancer AGS cells were cultured， and a nude mice transplanted tumor model was established. The nude mice were divided into the model group and MLCD low-， medium- and high-dose groups （150， 300， 600 mg/kg）. They were given distilled water or the corresponding drug solution by gavage once daily for four consecutive weeks. The size of transplanted tumors in nude mice was measured every six days， and the tumor volume was calculated. After the medication， the nude mice were sacrificed， and the transplanted tumor tissues were isolated. The contents of lactate dehydrogenase （LDH） and reactive oxygen species （ROS） in the transplanted tumor tissues were detected， and the changes in mitochondrial membrane potential were assessed. The pathological morphological changes were observed. The enzymatic activities of caspase-3， caspase-8， and caspase-9， as well as protein expressions of Fas and FasL and mRNA expressions of caspase-3， caspase-8， caspase-9， Fas and FasL in the transplanted tumor tissues， were detected. RESULTS Compared with the model group， the volume of transplanted tumors in nude mice from all MLCD dose groups was reduced to varying degrees. The contents of LDH and ROS， as well as the enzymatic activities of caspase-3， caspase-8 and caspase-9， were significantly increased/enhanced. The mitochondrial membrane potential was significantly decreased. The protein expressions of Fas and FasL， and the mRNA expressions of caspase-3， caspase-8， caspase-9， Fas and FasL were significantly up-regulated. Most of these differences were statistically significant （ P ＜0.05 or P ＜0.01）. Pathological results showed that with increasing doses of MLCD， the cellular density in the transplanted tumor tissues gradually decreased， and typical morphological features of apoptosis， such as loosening and increasing fragmentation， became more prominent. CONCLUSIONS MLCD can induce apoptosis in transplanted tumor cells of nude mice， and its mechanism may be related to the activation of the Fas/FasL pathway and the caspase apoptotic pathway.