As a potential radiosensitizer, magnolol not only enhances radiation‐induced tumour growth inhibition, apoptosis, and the levels of anti‐tumour immune cells, including CTLs, M1 macrophages, and DCs, but also highlights the inhibitory effects of radiation on immunosuppressive cells and proteins, such as Tregs, MDSCs, IDO, and VEGF. Here, IDO1 is linked to neoplasm.