Plant factories daily produce large amount of high quality vegetables under artificially controlled environments. One of the important issues to be considered is to establish suitable storage systems to achieve an acceptable length of shelf life and to minimize the risk to foodborne illnesses. This study deals with the application of the supercooling technologies (cooling below the freezing point without phase change) to the extension of the shelf life of the high quality leaf lettuces produced by the plant factories. The followings were found through the experimental study. The freezing temperature of the leaf lettuces of the plant factories is around -0.2℃ and the nucleation temperature of the leaf lettuces is between -1.0℃ and -6.1℃. The type of packages affects the characteristics of the supercooled lettuce by controlling the cooling rates and to reduce the risk of being frozen in the supercooled state. It was also shown that the lettuces under supercooled conditions keep the initial state of the water and sugar contents by reducing the respiration rate, and that the risk of foodborne illness is improved by keeping the number of the bacteria in low level even after the supercooled storages for three weeks.