The inhibitive activity of Kluyveromyces marxianus against citrus green mold caused by Penicillium digitatum Sacc. was investigated, as well as its effect on the activities of polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonium-lyase (PAL). The results showed that the treatments of washed cell suspension and living cell suspension have better inhibiting effect, as compared to the control treatment; while the culture filtrate and autoclaved cell suspensions could exacerbate green mold decay. The application of K.marxianus could induce higher PPO, POD and PAL activity as compared to the control. It was suggested that the biocontrol mechanism might be competitive for nutrition and space, and contribute to the secretion of antagonistc substance.