Chile is a country that presents a variety of thermal environments under which diverse species of amphibians reside. For these, the environmental temperature (Ta) is important since it affects their body temperature (Tb). Due to the high phenotypic plasticity of this taxa, the aclimation temperature to which they are exposed in captive conditions can influence their thermal responses. In addition, body size and/or mass may influence such behavior, and therefore, sexual dimorphism may differentiate Tc. Based on the above, Pleurodema thoul is an optimal object of study to evaluate thermal behavior since it presents sexual dimorphism in body size, and a strong influence of acclimation temperature on behavior. To analyze this association, individuals were collected in the commune of Antuco (Biobio Region) and subjected to two acclimation temperatures (10 degrees and 20 degrees C). Their size, mass, Tb and selected temperature (T-sel) were compared. The results show that in thermally homogeneous environments P. thoul is a tigmothermal species with a thermo-conformist behavior. The acclimation temperature did not present a significant effect on its behavior and they selected a wide thermal range with an average over 24 degrees C where there were no significant differences between the sexes.