In the current work, chryosphanol (MHAQ) was isolated and purified from rheum,and the photosensitization activities were studied. In nitrogen-saturated DMSO solution, irradiation of chryosphanol (MHAQ) with visible light (＞430 nm) produced the semiquinone radical anions (MHAQ°-), which was intensified significantly by an electron donor NADH, suggesting electron transfer between the excited and ground state photosensitizer molecules. In an air-saturated DMSO solution, superoxide radical anions (O2°-), trapped by DMPO, were detected.It was proved that O2°- was not originated from the singlet oxygen (1O2) but dependent on DMPO,chrysophanol, oxygen and the irradiation time. The singlet oxygen and °OH could also be produced by the photosensitization of the photosensitizer. These suggest that chrysophanol possesses the photosensitization activity via Type I mechanism and Type Ⅱ mechanism. To evaluate the photosensitization activities of MHAQ, emodin and mixed anthraquinone derivatives extracted from rheum, the relative productivities of O2°- were estimated to be 1.8, 1.1 and 1.0 respectively and the quantum yields for singlet oxygen to be 0.36, 0.53 and 0.14 respectively.Therefore, these low-cost pigments may be potentially used as phototherapeutic medicine for some kind of vascular diseases or photo-activated pesticides.