In order to evaluate the effect of different Trichoderma isolates on reducing the effects of drought stress on Polianthes tuberose flower, two factorial experiments were carried out based on a completely randomized design with three replications. In the first and second experiments, the first factors were Bi and 65 isolates of Trichoderma harzianum at three levels (0, 10, 20% v/v) and the second factor in both experiments was three levels of drought stress (25, 50, 100% field capacity). The results showed that both isolates increased biomass fresh and dry weights and root dry weight of Polianthes tuberosa plants exposed to stress conditions. Biomass fresh weight was increased by 4 g at 25% stress level by the isolate Bi and 14 g by the isolate 65, indicating the growth of this flower in the presence of Trichoderma fungus. The amount of proline in the treatment of isolate 65 at 20% stress level was increased compared to other levels of the fungus at 25 and 50% stress levels. Relative water content and leaf green area were enhanced when the two fungal isolates were applied under increasing stress levels. In general, it seems that the isolates Bi and 65 of Trichoderma harzianum have different effects under drought stress conditions. پرونده مقاله