Abstract: To investigate the synergistic inhibitory effect and mechanism of nisin and L-lactic acid against Aeromonas hydrophila,turbidity,plate count method,membrane electromotive force probe were used to detect the influence of nisin and L-lactic acid on growth,survival,biofilm formation,and membrane integrity of Aeromonas hydrophila(ATCC 35654,CICC 10500). The results showed that nisin and low concentration(3.5 mmol/L)of L-lactic acid synergistically inhibited the growth of two strains of Aeromonas hydrophila. And the inhibitory effect strongthened with the increasing of nisin concentration. The growth parameters modeled with a Gomptz equation showed that nisin and L-lactic acid synergistically prolonged the growth lag phase of Aeromonas hydrophila,the maximum specific growth rate decreased,and the maximum viable count of bacteria at stationary phase also decreased. Besides,nisin and L-lactic acid had a synergistic lethal effect on the indicator bacteria. Nisin and L-lactic acid treated for 12 h reduced the viable count of Aeromonas hydrophila. Results of the mechanism indicated that low concentration of L-lactic acid released the outer membrane LPS from the bacterial cells,and nisin further dissipated the membrane potential. The results would provide a theoretical basis for the use of nisin and L-lactic acid or their producing strains in control of Aeromonas hydrophila in aquatic products.