The growth of mung bean radicles decreased with the increase of NaCl concentration in incubationsolution, and the detected ultraweak photon emission intensity declined markedly as well. During germination of mung bean seeds, superoxide dismutase (SOD) activity also decreased as NaCl concentration increased. SODactivity was closely related to biophoton intensity. The results show that ultraweak photon emission detection is useful for the study of the plant response to salt stress.