Aims: To investigate the effect of tea polyphenol (TP) and Candida ernobii alone or in combination against postharvest disease (Diplodia natalensis) in citrus fruit and to evaluate the possible mechanisms involved. Methods and Results: TP at concentrations of 0 center dot 1%, 0 center dot 5% and 1 center dot 0% alone, or in combination with C. ernobii (1 x 106 CFU ml-1), showed a lower infection rate of stem-end rot. TP at the concentration of 0 center dot 5% or above significantly inhibited the spore germination of D. natalensis. TP at the concentration of 1 center dot 0% showed inhibitary ability on mycelium growth of D. natalensis. The addition of TP did not affect the growth of C. ernobii in vitro and significantly increased the population of C. ernobii in vivo. Conclusions: TP exhibited an inhibitory effect against D. natalensis and improved the biocontrol efficacy of C. ernobii. It was direct because of the inhibitory effects of TP on spore germination and mycelial growth of D. natalensis in vitro and indirect because of the increased populations of C. ernobii in vivo. Significance and Impact of the Study: The results suggested that TP alone or in combination with biocontrol agents has great potential in commercial management of postharvest diseases in fruits.