Changes in the body temperature (T_b) of reproductive females are well documented in squamate reptiles. However, the direction of these changes varies among species. Pregnant females may exhibit a lower or higher (and less variable) T_b than nonpregnant females. In some species, pregnancy has no detectable effect on female T_b. In this study, we compared the T_b of female rattlesnakes (Crotalus durissus) in different reproductive statuses (pregnant and nonpregnant) to investigate whether pregnancy influences T_b. We measured the T_b of female rattlesnakes kept in a semi-natural outdoor enclosure during summer and spring 2016 and summer 2017. Pregnant females selected a higher mean T_b than nonpregnant females. Moreover, we found significant differences in T_b among seasons. Body temperatures in summer 2017 were higher than in other seasons; however, reproductive status did not influence T_b variance. Therefore, our results agree with the hypothesis that females change their thermoregulatory behavior during pregnancy. Female rattlesnakes may increase their T_b during pregnancy to increase offspring fitness or to maximize their lifetime fitness.