In this study， casein (CN) was glycosylated with galactose oligosaccharide (GOS)， fructooligosaccharide (FOS) and chito-oligosaccharide (COS) by wet Maillard reaction. Comparing the effects of three functional oligosaccharides on the structure and functional properties of casein， the most effective functional oligosaccharide for casein modification was selected. First， the grafting rate and browning degree of the glycosylated products were determined. Subsequently， the microstructure of the glycosylated products was characterized using scanning electron microscopy (SEM)， sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)， a nanoparticle size analyzer， Fourier transform infrared spectroscopy (FTIR)， and ultraviolet spectroscopy. Finally， the functional properties of the glycosylated products were evaluated. The experimental results show that the grafting degree of CN-FOS was (29.9±0.65)%， CN-GOS was (33.5±0.76)%， and CN-COS was (34.2±0.27)%. With the increase of grafting degree， the properties of casein change significantly， especially the change of CN-COS， and the particle size decreases by about 344 nm. The solubility increases in a wide pH range， the highest value at pH 11 was (94.82±0.93). Meanwhile， its foaming activity was 226%， an increase of 58.3%， and emulsification activity was 20.18， an increase of 1.26 times. The sugar-glycosylated products of CN-COS showed 64.72%， 65.95%， and 32.38% scavenging rates against DPPH， ABTS， and ·OH free radicals， which increased by 3.35 times， 1.74 times， and 2.48 times respectively. The results indicate that COS demonstrates the most effective modification of CN. This study provides theoretical reference for the modification of casein by functional oligosaccharides and its application in food industry.