With the methods of in vivo and in vitro,the potential enhancement of Kluyveromyces marxianus by ammonium molybdate (NH4Mo) to control green mold caused by Penicillium digitatum on citrus fruit was investigated.Meanwhile,the effect of NH4Mo on growth and proliferation of K.marxianus was tested.The results showed that NH4Mo at different concentration did not inhibit the growth and proliferation of K.marxianus in culture medium or wounds of citrus fruits.The combination of K.marxianus and NH4Mo had suppressive effect on green mold caused by P.digitatum.Treatment of citrus fruits with K.marxianus plus NH4Mo (1 mmol/L) resulted in a consistent biocontrol activity,the disease incidence after 3 and 6 days were 28.33% and 60.00%,respectively.While the control treatment resulted in a disease incidence as high as 93.33% and 100%,suggesting that the combination of K.marxianus with NH4Mo may have great potential against green mold of citrus fruits.