This study evaluated the quality characteristics of Flammulina velutipesduring storage using modified atmosphere films of different thicknesses (20, 40, and 60 μm). The films included high-density polyethylene (HDPE) and low-density polyethylene (LDPE). F. velutipeswere stored at 1°C for six weeks, and quality was assessed based on weight loss, respiration rate, firmness, color parameters, β-glucan content, total phenolic content (TPC), and antioxidant activities (2,2-diphenyl-1- picrylhydrazyl and 2,2'-azino-bis [3-ethylbenzothiazoline-6-sulfonic acid] radical scavenging activities). All HDPE and LDPE films were more effective than the conventional film (polypropylene) at maintaining mushroom quality, particularly in the later stages of storage. In particular, LDPE films with thicknesses of 20 and 40 μm showed superior performance at reducing respiration rates and weight loss, while mushrooms packaged with these films retained higher TPC and antioxidant activities. The β-glucan content also remained more stable in mushrooms stored using HDPE and LDPE films. Although we did not evaluate changes in sensory properties or nutritional components, such as vitamins, our results suggest that the type and thickness of packaging films significantly influence the preservation of the quality of F. velutipesduring storage. Additionally, LDPE films with thicknesses of 20 and 40 μm were found to be the most suitable packaging materials for the distribution and storage of F. velutipes. Furthermore, these findings are expected to provide valuable insights into the selection of optimal packaging materials to extend the shelf life and maintain freshness during the postharvest handlingof F. velutipes.