Polylactic acid is a biodegradable material. In order to explore the effect of polylactic acid (PLA) film on fresh keeping of daylily flowers, an experiment was carried to determine if the PLA film thickness affected the preservation effect of daylily flowers with the polyethylene (PE) film as a control. The relevant quality indexes of daylily flowers were periodically recorded at (25±1)℃. The results showed that a gas condition with less oxygen and more carbon dioxide was formed inside the PLA film due to its lower O2 and CO2 penetration rate compared to the PE film. Such a gas condition inhibited the respiration of daylily flowers and obviously slowed the declining of soluble protein, soluble sugar, chlorophyll and ascorbic acid (Vc) contents in daylily flowers. The gas condition also inhibited the rising of permeability of cell-membrane and peroxidase (POD) activity during a storage period, which obviously prolonged the daylily flower storage time to 12 d , longer than 9 d of PE films. PLA film with 25 μm thickness showed the best preservation result.