Objective: Explore the influence of L-Arg on immune function of basketball players. Method: Select 20 basketball players of the school as the objects of study, and randomly divide them into control group and experimental group, with 10 students for each group. The control group takes the same amount of placebo, while the experimental group takes L-Arg capsule, three times a day, with the dose of 15g for each time. The experimental period is two weeks. Observe the influence on immune functions of two groups of players after the experimental period. Result: After a lot of exercise of players in two groups, C3 value sees obvious change, with obvious rise for the experimental group, and obvious decline for control group. The comparative results show significant difference (p􀀀0.05). For C4 value, experimental group shows unobvious change before and after the experiment, while control group shows obvious change. But there is no statistical significance (p􀀀0.05). After intensive exercise, IL-2 changes significantly and S-IL-2R concentration declines in serum of the basketball player taking L-Arg, which shows significant difference compared with that before exercise (p􀀀0.05). TNF-α shows unobvious change in experimental group and control group. Conclusion: Taking L-Arg contributes to improving players’ immune functions, and plays an important role in maintaining the stability of players’ immune functions.