Abstract: To investigate the effect of melatonin treatment on maintaining the freshness of fresh-cut purple cabbage, the study used purple cabbage as the subject and stored it under conditions of 4 °C and 85% RH for 12 d. Melatonin was used to treat fresh-cut purple cabbage at concentrations of 0, 0.01, 0.1, 0.5, and 1 mmol/L. Subsequently, the most effective concentration of melatonin was identified based on changes in color, weight loss, firmness, and the total number of aerobic bacteria. Furthermore, the influence of optimal melatonin concentration on the nutritional quality and antioxidant capacity of the fresh-cut purple cabbage was further evaluated. Results showed that 0.5 mmol/L melatonin treatment effectively reduced the decrease in lightness and redness, as well as the increase in yellowness, weight loss, softening, and the total number of aerobic bacteria in the fresh-cut purple cabbage (P<0.05). Additionally, fresh-cut purple cabbage treated with 0.5 mmol/L melatonin significantly enhanced the accumulation of anthocyanins (P<0.05), markedly inhibited the degradation in total glucosinolate content (P<0.05), and slowed the decrease of myrosinase activity, as well as the contents of sulforaphane and indole-3-carbinol. It also improved antioxidant activity by increasing DPPH and ABTS⁺ radical scavenging capacities, enhancing superoxide dismutase activity, and delaying the decrease in both catalase and peroxidase activities. In conclusion, 0.5 mmol/L melatonin treatment effectively maintained the nutritional quality and antioxidant capacity of fresh-cut purple cabbage, thereby providing a theoretical basis for the application of melatonin in fresh-cut vegetables.