Abstract: Collagen was extracted from chicken lung by acid extraction and ultrasonic-assisted acid extraction,then its properties and moisture retention were studied. Amino acid analysis of chicken lung collagen extraction showed that the composition was basically similar,the content of glycine was the highest(24.12% and 23.93%),and the imino acid content was the second,19.74% and 22.28%,respectively. The UV absorption peaks of acid extraction and ultrasonic-assisted acid extraction were respectively at 229.0 and 224.9 nm. SDS-PAGE showed that the two collagen extraction contained α₁ chain,α₂ chain,a small amount of β chain and γ chain. Fourier transform infrared spectroscopy and X-ray diffraction pattern showed that the collagen molecules extracted by the two methods were compact and maintained their original triple helix structure,indicating that the structure of collagen remained intact during ultrasonic-assisted acid extraction. The triple helix structure was not destroyed. The isoelectric point of acid extracted collagen was 7,the particle size distribution was around 340 nm,the isoelectric point of collagen by ultrasonic-assisted acid extraction was 6,and the particle size distribution was around 295 nm. With the solubility of collagen,it could explain that ultrasonic-assisted acid extraction could destroy the hydrogen bonds of collagen and change the particle size and aggregation morphology of the protein. SEM showed that the collagen structure of ultrasonic-assisted acid extraction was continuous and porous,and the particle diameter was significantly reduced. The water absorption and water retention of ultrasonic-assisted acid extraction collagen were 1.25 times and 1.17 times that of conventional acid extraction collagen respectively when placed for 24 h. In summary,ultrasonic-assisted acid extraction did not destroy the unique triple helix structure of collagen. The collagen had better solubility and moisture absorption by changing the hydrogen bond and the particle size of the protein.