In this paper,the inhibition of the fermentation product of Trichoderma longibrachiatum ST-27 on Streptococcus agalactiae was studied by a spectrophotometry and agar diffusion method.The results showed that the dichloromethane extract from T. longibrachiatum ST-27 fermentation product had obvious inhibitory effect on S. agalactiae,and the minimum inhibitory concentration (MIC) value was 0.312 mg/mL.It was found that the extract had an important effect on the biofilm formation of S. agalactiae. From scanning electron microscope (SEM) images,it was observed that most of the cells of S. agalactiae treated with dichloromethane extract had obvious folds or even ruptures on their surface.Compared with the clinical common antibiotics,the extraction of dichloromethane has obvious advantages in antimicrobial activity.As a substitute for traditional antibiotics,the results of this study have great application potential in inhibiting S. agalactiae.