In this study we aimed to evaluate the physiological variables of sheep under the influence of Piauí semi-arid environment. We used ten Santa Ines rams with black coat. The study was conducted at the small ruminants sector of the Federal University of Piauí, Campus Professora Cinobelina Elvas. Respiratory and cardiac frequencies, rectal temperature and sweating rate were measured. Temperature, air relative humidity and globe temperature and humidity index were recorded at the Campus weather station. There was a significant difference for all the meteorological variables so that the highest values were observed for the afternoon shift, except for air relative humidity (33.52%). For physiological variables significant effect was observed for respiratory and cardiac frequencies and higher values of these variables were found in the morning shift, with 49.50 breaths/min and 89.52 breaths/min, respectively. For rectal temperature, significant effect was observed, with the highest values for the afternoon shift (39.92 °C). We can notice that the animals needed to activate their physiological variables to keep their bodies in thermoneutral zone.