In order to find the causes of microbial contaminations and prevent microbial contamination, the cause analysis, handling methods and preventive measures of microbial contamination in fermentation processes were discussed.The results showed that during the fermentation processes of antibiotic products, sterilization of culture media, processing equipments, adjacent transfer pipes and ancillary systems should be adequately conducted with tight controls in order to ensure the related process steps  , prevent  bacterial contamination.