Abstract: Objective　To investigate the microbial contents presented on the surface of mucosa in the oral cavity of patients who accepted radiotherapy, and to provide the evidences of controlling post-radiotherapeutic infections.Methods　32 patients (19 males and 13 females) aged from 37~72 received radiotherapy after oral squamous cell carcinomas operationwere selected. Sam- ples of salivawere obtained fromthe radiated center and opposite mucosa before and after radiotherapy. The detective amount, de- tective ratio and constituent ratio were analysed by cultivation and identification.Results　Streptococci, Candida albicansand Pseudomonas aeruginosasignificantly increased on both sides of the oral mucosa whileNeisseriaandActinobacillusdecreased on radiated region after the radiotherapy.Conclusion　Radiotherapy has great effects on oral bacteria and pathogenic organism may play a role in post-radiotherapy infections. It is necessary to do bacteria culture and choose sensitive antibiotics regularly for post- radiotherapeutic patients.

Key words: oral carcinoma, radiotherapy, oral bacteria group