Three recombinant GH5 endoglucanases chosen for their contrasting hydrolytic activities, and a commercial endoglucanase were used to treat cellulose nanofibers (CNFs) after they were milled from bleached eucalyptus pulp with a supermasscolloider. This enzyme “post-treatment” resulted in different properties for the CNFs depending on enzyme treatment. The degree of polymerization, water retention value and enzymatic digestibility were used to estimate the extent of fibrillation. Morphologies of CNFs were observed by SEM and TEM. Electron microscopy images indicated endoglucanase post-treatment could efficiently improve the nanosize uniformity of CNFs from supermasscolloider fibrillation. All GH5 endoglucanase post-treated CNFs had a diameter between 3 and 19 nm with 70–89 % between 5 and 9 nm. The recombinant GH5 with no reported activity on crystalline cellulose was the most aggressive of the GH5s studied in reducing the DP of CNFs.