Silica with small and regular pore sizes was synthesized by hydrothermal crystallization and investigated with thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, N-2 adsorption-desorption, and scanning electron microscopy (SEM). The ethylene polymerization was carried out with the silica-supported metallocene catalyst, and the morphology of the resultant polyethylene was investigated with SEM. It was found that the silica could break up into sheet fragments instantaneously during polymerization and the polyethylene could replicate it to obtain nanosheet polyethylene. A possible formation mechanism of the nanosheet polyethylene is proposed.