Objective To investigate small intestinal absorption behavior of oral collagen peptides microspheres in rats. Methods The everted gut sac (EGS) and Single-pass intestinal perfusion (SPIP) model were established in Wistar rats (250-350 g, 5 months).The absorption of collagen peptide in different segments of rat small intestines was detected by BCAmethod. Results The cumulative transmittance of different particle size of calcium alginate/ Chitosan (SA/ CTS) microspheresin EGS experiments was that 500 μm microspheres<200 μm microspheres<10 μm microspheres ( P<0.01, except the jejunumintestine).The cumulative transmittance of microspheres ( 10 μm) was: SA/ CTS rate ( Ka ) and permeability rate ( Peff )microspheres> SA microspheres(duodenum segment, jejunum segment P<0.05;ileum segment, P<0.01).The absorption rate ofSA/ CTS microspheres was evidently higher than that of SA microspheres in SPIP experiments. Conclusion Small intestineabsorption of collagen peptides microspheres is correlated with particle size, and the chitosan in SA/ CTS microspheres isbeneficial to the absorption of collagen peptide in small intestine segments.