The effect of chitosan–ergothioneine coating (CHER) on the post-mortem quality and shelf life of Japanese sea bass (Lateolabrax japonicas) stored at 4 ± 1 °C for 16 days was investigated. Four different treatments were used: control without coating, CH with chitosan coating, ER with 0.3 % ergothioneine immersion, and CHER with chitosan containing 0.3 % ergothioneine coating. Sea bass pH value, total volatile basic nitrogen, peroxide value, thiobarbituric acid-reactive substances, biogenic amines, color, texture profile, and microbiological and sensory qualities were measured. The results indicate that treatment with CHER coating inhibited increase of total volatile basic nitrogen, peroxide value, and TBA value; maintained tissue hardness; and reduced microorganism counts, such as Pseudomonas, compared with control treatment. The efficiency was better than that of ER or CH treatment. Furthermore, sea bass treated with chitosan–ergothioneine coating also exhibited a positive effect, causing low biogenic amine content, especially putrescine, cadaverine, and histamine. Sensory evaluation proved the efficacy of chitosan–ergothioneine coating by maintaining the overall quality of sea bass during the storage period. Our study suggests that chitosan–ergothioneine coating might be a promising candidate for maintaining sea bass quality and extending their shelf life.