The thermal tolerance of four isolates of Beauveria bassiana and one isolate of Beauveria pseudobassiana was evaluated in vitro, by measuring the colonial diameters, on PDA medium, at temperatures between 5 and 35 ° C, during 14 days. The data obtained were used to calculate the growth rate of fungal colonies (mm / day), using linear regression. The representation of the values corresponding to the minimum, optimal and maximum temperature for vegetative growth was a curve described by a modified beta (ß) mathematical function. The minimum growth temperature of these isolates varied between 3.4 and 4.5 °C, the optimum temperature varied between 21.8 and 22.9 °C, except for one isolate of which optimal temperature was 26.8 °C, while the maximum temperature was varied for all isolates between 35.0 and 35.7 °C.