Abstract: The polylactic acid( PLA) film was applied to preserve Hass avocado fruits,with polyethylene( PE) film packaging and without packaging as controls.During the storage period(( 17 ± 2) ℃,RH 50% ± 5%),combining with O₂ and CO₂contents inside of the packaging,the preservation effect on avocado fruits was evaluated by the changes in their weight,color,firmness,chlorophyll,soluble solids and the enzyme activity.The results showed that one gas condition,containing less oxygen and more carbon dioxide,formed inside of the PLA film due to its own lower O₂ and CO₂transmission rate.This condition inhibited the respiration of avocado fruits so those packaged in the PLA film could be kept fresh longest. The storage time of this condition was 8 days,while the avocados packaged in the PE film and without packaging could be stored for 6 and 4 days.After 4 days,the avocados in the PLA film were most brightly colored. The firmness and chlorophyll content of them were 133.1 N and 1.28 mg / g respectively,higher than 85.5 N and 1.06 mg / g of those in the PE film. Furthermore,the avocados in the PLA packaging had lower peroxidase activity than the two other packaging. Therefore,the PLA film can prolong the storage time of Hass avocado,and this method is simple and safe to eat.