AbstractNanocrystalline cellulose (NCC) was used to improve the anti-yellowing property of polyurethane (PU). The NCC was modified with 3-glycidoxypropyltrimethoxysilane (GPTMS) to enhance its compatibility with PU, and the surface-modified NCC was characterized by contact angle (CA), X-ray powder diffraction (XRD), and thermogravimetric analysis (TG). NCC/PU composite was examined by scanning electron microscopy (SEM), Fourier transform infrared spectrophotometer (FT-IR), and X-ray photoelectron spectroscopy (XPS). Anti-yellowing property of the NCC/PU composite was determined using the Chinese National Standard GB/T 23999-2009. The results showed that the CA between modified NCC and PU was decreased by 26.6% (with 8% GPTMS). The crystal structure of NCC was inconspicuously affected by the surface modification, while the thermal stability of modified NCC was enhanced by 5.5%. The surface-modified NCC particles were homogeneously dispersed in the PU (as shown in the SEM micrographs). FT-IR and O1s XPS survey spectra of NCC/PU composites indicated the oxidation of hydroxyl groups and the production of carbonyl groups, while the photochemical degradation of PU resulting from UV radiation was prevented by the addition of NCC. The anti-yellowing property of the NCC/PU composite with 1.5% surface-modified NCC was increased by 57.7% and the contribution was decreased when the content of modified NCC was 2.0%.