New studies on cellulolytic enzymes aiming to improve biofuels production lead to a concern over the assaying methods commonly applied to measure their activity. One of the most used methods is Ghose's cellulase and endoglucanase assay, developed by the International Union of Pure and Applied Chemistry in 1987. Carrying out this method demands high volumes of reagents and generation of high amounts of chemical residues. This work aimed to adapt Ghose's methodology to reduce its application cost and residue generation and validate the adjustments. To do so, International and Brazilian laws were applied to validate methodologies. Method's modifications were successfully validated according to all institutions and were considered linear, accurate, precise, and reproducible. It was possible to reduce the volume of reagents and residues in 12 times. Considering the routine work of most laboratories, it is a great reduction on material costs and residue treatment, which reflects in sustainability and environmental impacts.