Background: Hypomagnesaemia may occur during training and competition as a result of poor dietary intake and excessive sweat loss. No study has yet explored serum magnesium (serum Mg) levels among Saudi athletes. Aim: To assess levels of serum Mg in young Saudi soccer players. Methods: A cross-sectional design was used in this study. A total of 34 young Saudi soccer players were included in the sample, and the height, weight, and skinfold measurements of each player were recorded. A single blood sample was taken from each player on a day on which they had participated in a training session, and the serum magnesium in the samples was then analyzed. A descriptive data analysis was used. Results: The data show that the mean of serum magnesium concentration was 0.83 ± 0.20 mmol/L, and concentration varied between a minimum of 0.23 and a maximum of 1.41 mmol/L. Discussion: The results of this study show that Mg concentration in the sampled athletes’ blood was normal. Further research should take blood samples on several days where the athletes are either between competitions or engaged in competitions, or are exercising at different levels of intensity.