Understanding the function of Trichoderma species in the control of Phytophthora drechsleri in pistachio orchards is very important. In this study, the effects of liquid extra-cellular secretions and volatile compounds secreted by 27 isolates of Trichoderma harzianum, T. crassum, T. koningii, T.aureoviride, T. asperellum, T. brevicompactum, T.longibrachiatum and T. virens were investigated on Phytophthora drechsleri growth and zoospore production. Due to cell wall combination of P. drechsleri, the ability of Trichoderma isolates in the production of β-1,3 glucanase and cellulase was evaluated in media with different carbon sources. The inhibitory effects of the 16 isolates of Trichoderma from growth of P. drechsleri were examined in a dual culture test. The results showed that Trichoderma isolates had a variable effect on the growth and zoospore production of P. drechsleri. Trichoderma harzianum-136 and T. harzianum-8279 revealed the highest inhibitory effect on radial growth of P. drechsleri in 20 and 30 percent concentrations of liquid extra-cellular secretions, respectively. Both isolates also showed the highest inhibitory effect on zoospore production of P. drechsleri in 10 percent concentration of extra-cellular liquid secretions. In the volatile compounds test, T. harzianum-8279 had the highest effect on the growth of P. drechsleri. In all Trichoderma isolates, the activity of β-1,3 glucanase was higher than cellulase activity. The enzyme production was also higher in the liquid medium containing the cell wall of P. drechsleri compared to glycerol as a carbon source. The highest activity of β-1,3 glucanase and cellulase was observed in T. harzianum-8279. Manuscript profile