Selenium (Se) is an essential trace element involved in several biological pathways, naturally found in rocks, soils, and food. Even though the daily requirement of Se is achieved through a balanced diet, the use of Se supplements has been frequent. Due to the risk of toxic effects of having Se in excess, supplementation is still under debate. The aim was to evaluate the effects of long-term Se supplementation upon systolic blood pressure (SBP) and redox status of rats exposed to sodium selenite. Male Wistar rats were exposed to 2 and 6 mg/L of sodium selenite in drinking water for 85 days. SBP and body weight were evaluated weekly; oxidative stress biomarkers were measured in blood or plasma; and Se levels were assessed in blood, plasma, kidney, and liver. Se supplementation (2 and 6 mg/L) induced significant increase in the SBP in rats from the 42nd day until the end of the study. This increase on SBP was not associated with significant changes in oxidative stress biomarkers. A significant increase in Se levels was found in whole blood, kidney, and liver from both groups of rats receiving Se supplementation when compared to control. Although the exact mechanisms underlying this augment in SBP are not clear, they are potentially related to other Se biological routes besides the synthesis of selenoproteins, such as GSH-Px. Due to the negative effects upon blood pressure, precautionary measures are advised, since the selling of supplements does not require a medical prescription.