In order to investigate the possibility of reducing the negative effects of late-season heat stress using phosphate-solubilizing bacteria, this experiment was carried out as split factorial based on a complete randomized block design with three replications in Haftkel city, in growing season 2016-2017. The main factor consisted of planting date in two levels and the sub factors as a factorial consisted of five bread wheat cultivars and of two levels application of phosphate solubilizing bacteria . The results showed that with delay in planting and occurrence of heat stress in grain filling period, grain yield, biological yield, harvest index and effective grain filling period decreased and grain filling rate increased and the reaction intensity varied depending on the cultivar. Mehregan cultivar had high yield in both planting dates and in the delayed planting date with the highest increase in grain filling rate and the lowest decrease in number of seeds per spike, had the highest grain yield and harvest index. By inoculating the seeds with bacteria, on both planting dates, the number of seeds per spike increased by 4.6%, grain yield by 7.6% and biological yield by 7%, but the effect of phosphate solubilizing bacteria on mitigating the effect of heat stress was not proven and the positive effect of bacteria was the same on both planting dates. Overall, higher ability to increase grain filling speed and maintain more grain number per spike were identified as two important traits for achieving higher grain yield under late-season heat stress conditions.