Leaf senescence is a typical symptom of heat injury in cool-season grasses during summer, which affects their overall turf quality and growth. Some phytohormones may regulate the timing and severity of senescence. The objectives of this project are to examine the changes of three major senescence-related phytohormones (cytokinins, ABA and ethylene) under heat stress in two Agrostis species that differ in their heat tolerance, and to determine the relationship between hormonal changes and heat-induced leaf senescence. The plants of heat tolerant A. scabra and heat sensitive 'Penncross', a cultivar of A. stolonifera, were exposed to the optimum temperature of 20°C and superaoptimal temperature of 35°C for 5 weeks. The amount of cytokinins, IPA and ZR, declined in both species, but the decrease in A.scabra was less than that in 'Penncross'. On the other hand, ABA and ethylene contents increased in both species exposed to high temperature. However, while the increases in 'Penncross' started from the beginning, the increase of ABA and ethylene in A.scabra was postponed for two and three weeks, respectively. Besides, A. scabra exhibited slower decrease in its turf quality, photopigment contents, and chlorophyll fluorescence, as well as a slower growth rate. Our results suggest that the better tolerance of A.scabra to high temperature could be due to its ability to maintain normal metabolism of hormones for a longer time, which could be involved in delaying leaf senescence.