Agricultural crop affected preliminary and the most prominent by the adverse effects of global climate change have to adapt to various abiotic factors that will occur as a result of climate fluctuations in the near-future and struggle to survive. Among abiotic factors, the one of the greatest impact on plant stress is high temperature. Therefore, the most important step to take action against the global threat is the development of new temperature tolerant varieties. Barley, which is the fourth most important cereal in the world after wheat, maize, and rice are affected by high ambient temperatures. In this work, the effects of their alone and in double, triple combinations of ten various plant growth regulators (PGRs) on mitotic activity and chromosome behaviors in root meristems of barley exposed to high temperature (30°C) were investigated. In the experiments, Hordeum vulgare L. cv. Bülbül 89 variety and GA3, KIN, BA, E, EBR, TRIA and PAs (Spm, Spd, Put, Cad) as growth regulators were used. The results obtained were compared with each other and with those of the seeds germinated at optimum temperature (20°C). Consequently; it has been determined that most of the PGRs studied, especially the GA3 and their combinations with GA3, exhibit a very successful performance on mitotic activity and cytogenetic aberrations in barley seeds germinated under high temperature stress-HTS conditions. The effects of these PGRs (except for EBR) and their combinations on mitotic activity and chromosome behaviors under HTS have been presented in this study for the first time.