The present invention relates to a composition for preventing or treating an immune-related disease, and, more specifically, relates to a composition for preventing or treating immune-related diseases or oxidative-stress-related diseases in which the toxicity of an arsenic compound is effectively suppressed while the immune function boosting effect thereof is nevertheless maximised. The composition according to the present invention is useful in preventing or treating various immune-related diseases or oxidative-stress-related diseases since the composition reduces the toxicity of arsenic compounds, which traditionally have been difficult to use in clinical practice due to toxicity, while nevertheless maximising the pharmacological effects thereof.