For improving water solubility of hypocrellin B (HB), a cyclodextrin modified hypocrellin B (HBCD) was designed and synthesized. Electron spin resonance (ESR) measure ment indicated that this HB derivative remained photodynamically active in terms of type I and type II mechanisms. HBCD is water-soluble and possesses stronger photosensitized damage ability to calf thymus DNA than hypocrellin B.