Cellulose is one of the most abundant and renewable biopolymers sources of lignocellulose fiber. Lignocellulosic fibers are composed of three main components: hemicellulose (20–40 wt%), cellulose (40–60 wt%), and lignin (10–25 wt%), which are known to present very complex structures. The cellulose fibers submitted to acid hydrolysis gives the possibility to extract yield defect-free, rod-like crystalline residues called cellulose nanowhisker (CNs). Aside of having good physical and Chemical properties ‘this biopolymer calls attention because of their inherent renewability and sustainability in addition to their abundancy. They have been the subject of a wide array of research efforts as reinforcing agents in nanocomposites due to their low cost, availability, renewability, light weight, nanoscale dimension, and unique morphology. It is reported values for Young’s Modulus around 150 GPa and tensile strength of 7.5 GPa to cellulose nanowhiskers. These values are potentially ‘‘stronger than steel’’ higher than some materials traditionally used for making composites such as carbon fibers and Kevlar. The object of this work is to study the influence of H2SO4 concentration (30%, 45% and 65%), time dependence and concentration applying ultrasound to reaction system for extraction of cellulose nanowhisker using sisal pulp as raw material.The nanowhisker obtained is submitted to optical birefringence observation and to Transmission Electron Microscope analysis.