Actively growing Lactobacillus plantarum CGMCC 1.1856 cells totally inhibited the germination of mold spores. Cell-free supernatant broth from the fermentation of Lactobacillus plantarum could not destroy the viability of mold spore. While the pH of the culture broth and supernatant were about 4.0, and the acidification of non-fermented broth to pH 4.0 with lactic acid could not cause a similar inhibition on spore germination. This experiment discounted the possibility that the inhibitory effect on mold growth was due to the lactic acid produced by Lactobacillus, and suggested that the effect was because of both low pH and microbial competition.