NCC preparation using sulfuric acid hydrolysis from cellulase pretreated fibers was optimized in order to obtain the highest possible yield with 62% and 65% wt. sulfuric acid throughout two statistical plans. At optimal conditions (10U/g odp cellulase, 25 min hydrolysis, 47 ºC and 62 % wt. H2SO4) high yields were obtained (=80%) including an increase produced by enzyme of ~9 %. Optimal conditions produced nanosized particles of around ~200 nm with a reduced surface charge and sulfur content. The performed optimization allowed reducing the hydrolysis time in a 44%, and also increasing yield in more than 10% compared to results exposed in previous works. The effects of cellulase pretreatment were noticeable even under aggressive hydrolysis conditions, emphasizing its possibilities. Zeta potential and polydispersity indexes indicated that all studied conditions leaded to good quality final products, with values among -50 mV and 0.2, respectively. TEM analysis confirmed the presence of NCC and suggested morphological differences between samples. Finally FTIR analysis provided evidence that cellulase treatment increased crystallinity of both cellulose fibers and NCC, and also increased accessibility to fibers, supporting data obtained from NCC