Abstract: Using sturgeon and grass carp swim bladder as raw materials, compared and analyzed the physicochemical properties of two kinds of fish swim bladder pepsin-soluble collagen (PSC). Calculation of collagen yield, amino acid composition, SDS-PAGE, ultraviolet spectroscopy, Fourier infrared spectroscopy, circular dichroism, microdifferential scanning calorimeter to study the differences of the composition and physic-chemical properties of the two types of swim bladder PSC. The results showed that the content of crude fat and hydroxyproline in the basic nutrients of sturgeon swim bladder were significantly higher than that of grass carp swim bladder (P<0.05). The yield of sturgeon swim bladder was 80.63%, which was significantly higher than the PSC yield of grass carp swim bladder 49.85% (P<0.05).Two kinds of swim bladder PSC were consistent with type I collagen. The relative molecular weight of α chain and the content of dimer β chain of sturgeon swim bladder PSC were lower than those of grass carp swim bladder PSC. In the amino acid composition, the content of Ser, Met, Ile, Leu, His and Arg of sturgeon swim bladder PSC was significantly higher than that of grass carp swim bladder PSC (P<0.05), the content of Ala, Phe, Lys, Pro and Hyp of grass carp swim bladder PSC was significantly higher than that of sturgeon swim bladder PSC (P<0.05). They had similar secondary structures. The PSC denaturation temperature of sturgeon swim bladder was 29.26 ℃, which was significantly lower than that of the PSC of grass carp swim bladder, which was 36.01 ℃ (P<0.05). Among the two kinds of fish bladder PSC, grass carp swim bladder PSC had better thermal stability than sturgeon swim bladder PSC, but sturgeon swim bladder PSC had a higher yield than grass carp swim bladder PSC.