Abstract: To solve the problem of low efficacy due to volatility and water-insolubility of α-chlorocinnamaldehyde,its nanoemulsion was prepared by low energy emulsification in this study,followed by multiple evaluations on its quality,stability,antibacterial activity and biological safety. The results showed that the best formulations of α-chlorocinnamaldehyde nanoemulsion were chlorocinnamaldehyde 2.81%,olive oil 1.02%(oil phase),Tween-80 25%(surfactant),ethanol and 1,2-propylene glycol mixture 6.25%(v∶v=13∶12,mixed cosurfactant). Using this formulation,the prepared nanoemulsion was clear,transparent,and thermodynamically stable,and it could be diluted by water indefinitely. The particle size of this nanoemulsion was distributed ranging from 10 to 50 nm with an average particle size of 15.88 nm(polydispersity index=0.16). In comparison with chlorinated cinnamaldehyde,the antibacterial activity of α-chlorocinnamaldehyde nanoemulsion increased by 50%~200% and especially high concentration of nanoemulsion could eradicate bacterial biofilm. Through hemolysis test,it was showed that the biological safety of α-chlorocinnamaldehyde was improved significantly when it was nanoscaled. Taken together,it was concluded that nanoemulsification of α-chlorocinnamaldehyde could extend the application of chlorocinnamaldehyde in the field of food and medicine greatly.