Cinnamic acid was effective to control blue mold caused by Penicillium italicum in ‘Orah’ mandarins. The inhibition of fruit decay was positively correlated with cinnamic acid concentration. Cinnamic acid at 1.5mM, in combination with the biocontrol yeast Cryptococcus laurentii at 1×10⁷ cells/mL, provided synergistic effects against P. italicum. Population dynamic analysis demonstrated that the growth of C. laurentii in fruit rind wounds was not significantly influenced by cinnamic acid. C. laurentii multiplied rapidly, regardless of whether the yeast was used alone or combined with cinnamic acid. By contrast, spore germination and mycelial growth of P. italicum in the culture medium were markedly inhibited by cinnamic acid. By using propidium iodide fluorescent staining, loss of membrane integrity in P. italicum was observed after cinnamic acid treatment. Furthermore, cinnamic acid led to the leakage of cellular constituents including soluble proteins and carbohydrates from hyphae of P. italicum. These results indicated that the fungal pathogen P. italicum is more sensitive to cinnamic acid than the biocontrol yeast C. laurentii. Taken together, our data suggest that the enhancement in biocontrol efficacy of C. laurentii might be associated with the differential influence of cinnamic acid on the antagonistic yeast and the fungal pathogen.