Hypocrellin A (HA), an efficient phototherapeutic agent, can chelate with lanthanum ion to form a 1:1 complex, which exhibits enhanced O-1(2) generation quantum yield, a red-shifted absorption window, greatly improved water solubility, a much lengthened triplet excited state lifetime, and an increased affinity to DNA with respect to HA. These effects in turn lead to a more potent photodamage ability on calf thymus DNA for La3+-HA than HA in both aerobic and anaerobic conditions, indicating the potential application of La3+-HA in the field of photodynamic therapy (PDT).