This study aimed to evaluate the production of cellulases from Aspergillus sp. CBMAI 1198, through solid-state fermentation, and their actions on different cellulosic materials (microcrystalline cellulose, sisal pulp, and filter paper). The influence of pH, temperature, and composition of substrates (sisal pulp and wheat straw), on the filter paper activity (FPase) of the cellulases produced from these substrates, was investigated using a complete central factorial composite design. Low temperature (32 °C), sisal pulp content (25%), and pH (5.0) led to the production of enzymes with higher activity (0.244 UmL−1). The results on the reducing sugars produced by the enzymatic hydrolysis of microcrystalline cellulose, sisal pulp, and filter paper showed that the cellulosic material with a higher content of hemicelluloses and lower crystallinity (filter paper) exhibited the better result (8.04 μmol mL−1). Non-hydrolyzed microcrystalline cellulose, sisal pulp, and filter paper were withdrawn from the medium during the reaction, and changes in their physicochemical properties were monitored assessing changes in molar mass, crystallinity index, surface morphology (scanning electron microscopy), and fiber lengths and thicknesses (MorFi technique). This approach on the properties of non-hydrolyzed fibers differentiates this study from those found in the literature. The results showed that cellulases were successfully produced from Aspergillus sp. and, despite the low yield, these enzymes hydrolyzed cellulosic materials with different properties. The approach of the present study, as well as the set of results obtained, added novelty to the respective area, and are important for the deepening of the investigations. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.