Chitosan (CTS), a linear binary copolymer of (1→8)-linked 2-acetamido-2-deoxy-β-D-glucopyranose (GlcNAc unit) and 2-amino-2-deoxy-β-D-glucopyranose (GlcNH2 unit), is derived from chitin by alkaline deacetylation. In the present work, the narrow molecular weight distribution chitooligosaccharides were prepared by degraded CTS with a microwave-assisted-cleavage method of metal-coordinating template-absorption catalytic oxidation. Under physiological pH conditions, the interaction of CTS and the narrow distribution chitooligosaccharides with Human serum albumin (HSA) was preliminarily explored by fluorescence spectra. Low molecular weight CTS in different concentration was added into HSA solution respectively, the absorptivity of the HSA solution decreased considerably. This phenomenon indicated that there was an interaction between these six different low molecular weight CTS with HSA, and the smaller the DP of the narrow distribution chitooligosaccharides, the stronger the interaction with HSA. However, the interaction gradually failed in as the DP was less than eight. The interaction almost disappeared when using glucosamine, the final product of degraded CTS, which revealed that there was a scale effect between chain-like CTS molecule and protein biomacromolecule. The results suggest that the strongest interaction binding occurs in CTS with DP≈8. Whether the DP increases or decreases, the interaction will weaken.