The γ radiation level, alpha potential energy of thoron and alpha surface contamination level at a mantle factory in the east of Zhejiang Province are reported. The measured results show that the additional annual effective dose equivalent absorbed by the worker in some workshops of the factory was higher than 15 mSv—management limit. The alpha surface contamination on the workers' hands in some workshops was 10 times more than the management limit of National Standard (0.04Bq/cm²). The mantle factory's main danger to body was internal irradiation of α rays from thoron aerosol.