Abstract: A ?-glucan composition and use thereof. Specifically provided are uses of the ?-glucan composition in preparing a composition for improving or treating immune-related diseases, said ?-glucan being a ?-glucan containing ?-1,3 and ?-1,6 glucosidic bonds in the molecules thereof, and having a molecular weight of 1-50 kDa. The ?-glucan features a novel structure, a controllable mass, abundant sources, simple preparation processing, high product purity, strong biological activity, and is easy to produce industrially, among other strengths. The resulting water soluble ?-glucan composition features better antitumor activity, has the potential to be developed into a safe and effective novel drug for improving or treating immune-related diseases and fighting tumors.