Chitosan (CS) is a fragile material with a high modulus of elasticity. Improving its flexibility as well as membrane permeability are the key aspects that need to be addressed for using CS as a biomaterial. Poly(ethylene glycol) (PEG) has several unique properties such as protein resistance, low toxicity, immunogenicity, and good solubility in both water and organic solvents. In this study, a vinyl compound was grafted to the C-6 position of CS by protection-grafting-deprotection. The vinyl CS was then crosslinked with PEG dimethacrylate (PEGDMA) selectively at its C-6 position to form CS-g-PEG copolymer membranes. Analyses from spectra of Fourier-transform infrared and nuclear magnetic resonance confirmed the chemical structure of the crosslinking CS-g-PEG copolymer membranes. Thermal and mechanical properties of the prepared CS-g-PEG membranes were measured and well-correlated to their structures. The incorporation of PEGDMA into the CS increased the material’s flexibility and thermal resistance. Finally, the CS-g-PEG membranes were found to have good protein resistance and blood compatibility; therefore, it has potential application as the biomedical material especially for hemodialysis.