Abstract: Objective: To isolate lactic acid bacteria( LAB) from marine fish intestine with strong antagonistic activity against Pseudomonas fluorescens. Methods: LAB strains with inhibitory activity against P. fluorescens were screened using the method of Oxford cup agar diffusion. The strains were identified by biochemical tests and16 S rRNA sequence analysis. The antibacterial substance was determined using protease sensitivity test,p H test and heat- treated test. The integrity of cell structure of P. fluorescens treated with cell-free supernatants( CFS) of produced by LY1-6 was observed by scanning electron microscope. Results: Strain LY1-6 with outstanding inhibitory activity against P. fluorescens was screened from ocean perch intestine,and was identified as Lactobacillus sakei.The inhibitory activity of LY1-6 CFS was completely lost by treated with pepsin,meanwhile,when treated with neutral protease,papaya protease,trypsin and alkaline protease,the inhibitory activity lost38.22%,38.00%,22.48% and 18.46% respectively. The inhibitory substance was effective within p H2.5 ~ 5.0 and stability after thermal treatment,which was preliminary determined as bacteriocins. The scanning electron microscope images revealed that the integrity of cell of P.fluorescens treated with LY1-6 CFS was damaged and dissolved.Conclusion: Lactobacillus sakei LY1-6 with strong inhibitory activity against P.fluorescens was screened from ocean perch intestine.Moreover,its antibacterial substance was determined as bacteriocins.The mechanism of action was destruction the integrity of cell.Lb.sakei LY1-6 biological preservative can be used as starting strain for the control of P.fluorescens in aquatic products spoilage.