Sericite nanoflakes were prepared by exfoliating sericite layers by wet ultrafine grinding. Their appearance morphologies and main properties were characterized. Optimum conditions were studied with the purpose of forming shear stress which was beneficial to the exfoliation of mineral flakes. The results indicated that sericite nanoflakes could be prepared. Mass ratio of grinding media to materials, diameter ratio of grinding balls, solid content of powders and grinding time had significant effects on the preparation. The thicknesses of sericite nanoflakes were 20-80 nm, and the transmittances of ultraviolet ray with wavelength of 190-220 nm were only 0.1%-1%. This demonstrated that sericite nanoflakes had the function of shielding ultraviolet ray.