Manipulating cellulose molecules in nanosize range to create excellent nano materials is the frontier of cellulose science. Cellulose nanoparticles, a kind of renewable biomaterial, have become the research focus home and aboard. It is of great importance to develop a simple, green, low energy-consuming, rapid and efficient method to prepare cellulose nanoparticles. In the present paper, cellulose nanoparticles (CNP) which enjoy good dispersity and nanosize were prepared by alkaline hydrolysis in a simple and feasible way, with microcrystalline cellulose (MCC) as the raw material. Moreover, the size and morphology, crystal structure and spectrum properties of the cellulose nanoparticles were analyzed by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectrometry (FTIR). TEM images demonstrate that the prepared samples are in quasi-sphere shapes with good dispersity and with size about 20-40 nm. The SEM images of the samples show that the purified cellulose nanoparticles can be obtained after dialysis treatment to remove salt particles. The XRD results show that the microcrystalline cellulose and cellulose nanoparticles almost have the same diffraction peaks in cellulose I crystal form. Because of the damage of amorphous region of MCC by alkaline hydrolysis, the crystallinity of produced samples increases by up to 79.71%. The grain size was calculated with Scherrer’s formula, and the average size is about 3-6 nm. Furthermore, the FTIR spectra suggest that the characteristic peaks on the graphs of cellulose nanoparticles have no significant change compared to natural cellulose, which indicates that the sample remains as the basic chemical groups of cellulose. The results show that preparing cellulose nanoparticles (CNP) by alkaline hydrolysis enjoys the ease to operate and can produce high yield, and therefore the study offers a new approach to obtaining cellulose nanoparticles with nanosize and good dispersion.