Trisodium phosphate (TSP) has been shown to be effective for control of food-borne bacteria, but little is known about its activity against phytopathogenic fungi that cause plant diseases. Here we show that TSP application reduced disease development of brown rot caused by Monilinia fructicola on jujube and peach fruits. The efficiency of TSP was positively correlated with its concentrations. Analysis of the influence of pH on efficiency of TSP indicated that the inhibitory effect of TSP against M. fructicola was only partially influenced by its alkaline pH. TSP directly inhibited spore germination, germ tube elongation, and mycelial growth of M. fructicola in the culture medium. To further investigate the mechanisms by which TSP inhibited fungal growth, we detected the integrity of the plasma membrane of M. fructicola. Our result show that TSP treatment resulted in the loss of plasma membrane integrity, leading to the release of intracellular contents such as soluble proteins, carbohydrates, and nucleic acids. Taken together, our data suggest that TSP was effective for controlling postharvest disease caused by M. fructicola on jujube and peach fruits and this antifungal activity was directly related to the disruption of cell membrane of the fungal pathogen.