Nanocrystalline cellulose (NCC) has widely been used for miscellaneous applications due to its superior proprieties over other nanomaterials. The major problems associated with the production of NCC are long reaction time, low production rate and inefficient process. The mass production of NCC within short time remains a great challenge currently. The main objective of this study is to overcome the present problems by investigating the performance of a high pressure process (HPP) and a low pressure process (LPP) for NCC production from raw rice husk biomass (R-RHB) by chemical extraction. The general steps of chemical extraction are delignification, bleaching and hydrolysis. Delignification of R-RHB for HPP and LPP was conducted at 80 °C using stainless steel reactor and jacketed glass reactor, respectively. During the delignification in the HPP, 5 bar pressure was applied; while atmospheric condition was used for the LPP. Delignification of HPP and LPP was run for 12 hours using aqueous solution of NaOH (4M) for the separation of cellulose from R-RHB by the dissolution of lignin and other amorphous impurities. Delignified samples were collected after delignification reaction, then washed, bleached and finally hydrolyzed in order to convert cellulose to NCC. NaOCl (20%) and H2SO4 (4M) solutions were used for bleaching and hydrolysis processes, respectively. The resultant NCC products of HPP and LPP were analyzed by FTIR, XRD, SEM, EDX, AFM and TEM. The chemical composition of R-RHB and NCC was estimated by TAPPI methods to observe the product purity. High purity NCC has been produced in HPP with crystallinity approximately 55 % and production rate of 62% whereas LPP 51%. It was found that, while both processes produced NCC of diameter 10-20 nm and length 1-2 µm, the HPP was faster and more efficient than the LPP to produce quality NCC from R-RHB. Keywords: Nanocrystalline Cellulose, High Pressure Process, Low Pressure Process, Rice Husk Biomass