This study was performed to assess how magnesium supplementation affects plasma lactate levels at rest and exhaustion in sportsmen and sedentary. Research was performed on 30 healthy subjects varying between 18-22 years of age for a four-week period. Subjects were separated into 3 groups: Group 1; sedentary taking magnesium supplementation only (10 mg/kg/day) (Mg + S), Group 2; subjects magnesium supplemented + training 90-120 min 5 days a week (Mg + Training), Group 3; training 90-120 min 5 days a week. Lactate levels of the groups were measured 4 times; at rest and exhaustion in the beginning of the research and after the end of the research. At the end of the research, exhaustion measurements both before and after supplement were found significantly higher than rest measurements in terms of lactate levels (p<0.05). An important decrease was determined in the lactate levels of the 1 st and 2 nd groups when compared to their first measurements (p<0.05). The results of this research indicate that lactate increases with exhaustion. However, magnesium supplement may positively affect performance of sportsmen by decreasing their lactate levels.