Spotted seals (Phoca largha) is a critically endangered pinniped in China and South Korea. Captive in artificially controlled environment is a conventional method to protect and maintain the population of this species. However, little is known about the physiological differences between the wild and captive P. largha. In order to draw the preliminary protein expression profile in the P. largha, blood from the wild and captive pups were subjected to a label-free comparative proteomic analysis. According to the results, 972 proteins were identified, which performed functions related to various metabolic, immune and cellular processes. Among these identified proteins, the expression level of 51 proteins significantly changed between the wild and captive P. large pups. These differentially expressed proteins were enriched in a wide range of cellular functions, including cytoskeleton, phagocytosis. proteolysis, gene expression regulation and carbohydrate metabolism. The activities of phagocytosis and its related ubiquitin mediated proteolysis were significantly higher in the blood of wild P. largha pups than in captive individuals. In addition, a key protein associated with the differences in the wild and captive P. largha pups, heat shock protein 90-beta, were determined due to the most interactions of it with various differentially expressed proteins. Moreover, the wild P. largha pups could be more nutritionally stressed and have more powerful immune capacity. Our study provides the first data on the preliminary protein composition and gives useful information for the physiological characteristics research in this species.