It has been reported that Tetrandrine, a Chinese medical herb, could enhance the radiotherapy of primary lung carcinomas. The purpose of the study was to verify whether Tetrandrine is a potential radiosensitizer. The experimental results showed the drug was not able to increase effects of radiation on S-180 and Lewis tumors, with E/O less than 1.4 in all experiments. There was no evidence to prove that the immediate radioresponse of primary lung carcinomas to combination of radiotherapy and Tetrandrine was better than that of radiotherapy alone. Therefore, probably Tetrandrine is not a radiosensitizer.