AbstractIn the present study, the effect of exopolysaccharides (EPSs) extracted fromPseudomonas tolaasiion the growth ofPleurotus ostreatusmycelia was determined.P. ostreatusmycelia was cultivated with different concentrations ofP. tolaasiiEPSs, and their mycelial growth rate, protein content, and enzyme activity were measured and compared. The results showed that EPSs inhibited the growth ofP. ostreatus. The proline and vitamin C contents ofP. ostreatusincreased at an EPS concentration of 40%. The cellulase, α-amylase, protein, and glucose utilisation rates ofP. ostreatusgradually decreased with the increase in EPS concentration. Altogether,P. tolaasiiEPSs had a significant inhibitory effect on mycelial growth. Therefore, we concluded that in addition to tolaasin, EPSs may also be the virulence factors responsible for the pathogenesis ofP. tolaasii.