This study investigated the carboxymethylcellulose (CMC)-based edible coating effects on some quality parameters and enzyme activities of plum fruits (Prunus domestica L. cv. Golden drop) during their shelf life. Three concentrations of CMC (0.5%, 1%, and 1.5%), plasticized with glycerol (0.3% w/v), were applied to plum fruits plus a control treated with only distilled water. The results demonstrate that the CMC-based edible coating was significantly effective in maintaining firmness and titratable acidity (TA); vitamin C, anthocyanin, and flavonoid content; and the antioxidant capacity of plum fruits. Enzymatic activity was affected significantly by the coating. Peroxidase (POD) activity increased, and polyphenol oxidase (PPO) and polygalacturonase (PG) decreased. In general, the formulation consisting of 1% CMC showed the best results in most of the measured parameters. Taking into account the positive effects on qualitative and biochemical characteristics of CMC-based edible coatings on plums, their application can be a potentially promising method to enhance the shelf-life of this fruit.