The paper studied the preservation effect of lactic acid bacteria on fresh longan fruits and developed a composite bio-preservative agent with lactic acid bacteria as the main component. The formula of bio-preservative agents is 8.6×106 CFU/mL dgnkzx002, 1% kojic acid and 1% sodium lactate. Taking longan fruits (Dimocarpus longan Lour. cv. Dongfeng) as test materials, the influence of composite biological preservative of Leuconostoc mesenteroides on fruit quality and effect on fresh-keeping of longan fruits were evaluated during storage at 4 ℃. The results showed that titratable acidity (TA), soluble solids (TSS) and vitamin C (Vc) content of longan fruit treated by the composite biological preservative were 90.90%, 23.19% and 47.79%, respectively, higher than those by the water control group. The commodity rate and weight loss rates were 192.31% and 73.9%, respectively. This showed that the composite biological preservative could delay the decrease of total soluble solids (TSS), titrable acid (TA), vitamin C, reducing sugar and total sugar, reduce weight loss rate, and slow down the commodity rate of decline and inhibit polyphenol oxidase (PPO) activity, peroxidase (POD) activity, thus maintaining the activity of superoxide dismutase (SOD). Therefore, composite biological preservative treatment effectively maintained the quality of longan fruits and slowed down the process of enzymatic browning. The composite biological preservative of Leuconostoc mesenteroides showed great potential in longan biological preservation.