: Selenium (Se) is a trace mineral element with important roles in enhancing athletic performance and athlete recovery. : This study aimed to observe the differences in plasma, urinary, erythrocyte, and platelet Se concentrations between sexes and analyze the variations in Se concentrations during the soccer season. The main hypothesis was that significant differences in Se levels would be observed between male and female athletes and that these differences would fluctuate throughout the season due to varying training loads and nutritional factors. : Twenty-two male (20 ± 2 years; 1.76 ± 0.06 m; 14.73 ± 3.13 years' experience; fifth Spanish division) and twenty-four female soccer players (23 ± 4 years; 1.65 ± 0.06 m; 14.51 ± 4.94 years' experience; second Spanish division) participated. Three assessments were conducted during the season. Evaluations included anthropometry, body composition, fitness (cardiorespiratory and vertical jump), and nutritional intake. Venous samples of blood and urine were obtained. The concentrations of Se in the plasma, urine, erythrocytes, and platelets were analyzed through inductively coupled plasma mass spectrometry. : No differences in Se intake were observed. The Se concentrations in the plasma, urine, and platelets were found to be higher in males, while females showed elevated levels in their erythrocytes ( < 0.05). Throughout the season, plasma and platelet Se concentrations exhibited a progressive increase ( < 0.05). : Assessing Se status during the season is essential for evaluating nutritional supplementation to maintain performance given Se's vital role in the immune and antioxidant systems.