Сa²⁺ plays an important role in plant signal transduction. Heat stress induces elevation of Ca²⁺ level in cytosol. Pretreatment by different concentrations of calcium chelator EGTA didn’t affect the viability of A. thaliana cells at normal temperature, but slightly decreased at mild heat stress. Blocking of extracellular Ca²⁺ influx by EGTA inhibited induced thermotolerance and heat-induced expression and synthesis of Hsp101 and another heat shock proteins (HSP). The findings indicate the dependence of Hsp101 and another HSP synthesis from cell Ca²⁺ level.