In recent decades, dependence on fossil fuels resources has shifted into derivation of cellulose based materials to replace the non-renewable resources. Lignocellulosic biomass is the most abundant feedstock on earth and is one of the promising renewable and sustainable resources. In the present study, simple preparation of nanocellulose particles by using ionic liquid (1-butyl-3-methylimidazolium hydrogen sulfate) has been introduced by investigating the influence of reaction temperature (room temperature and heat treated at 90°C). The resultant samples were characterized using X-Ray Diffraction (XRD) and Fourier-Transform Infrared Spectroscopy (FTIR). Interestingly, it was found that the high crystallinity sample could be synthesized at temperature of 90°C. The reason might be attributed to ionic liquid enter into the space between cellulose chains and caused cellulose molecules progressively swelled up when heated. Consequently, amorphous regions of cellulose were dissolved by ionic liquid and crystalline parts of cellulose were leave in the cellulose structure. From the XRD data, it could be observed that sharper crystalline peak and higher crystallinity index (CrI) present within heat-treated samples which corresponded to higher crystalline structure of cellulose I. While the broader peak and lower CrI of untreated cellulose samples indicated lower crystalline structure of cellulose I. Pretreatment of cellulose with ionic liquid can provides a facile approach for the preparation of nanocellulose particles with high crystallinity.