White rot fungi, primarily belonging to Basidiomycota phyllum, efficiently degrade lignocellulose by producing a diverse array of enzymes capable of breaking down the complex matrix of lignin, cellulose and hemicellulose into available sugars, supporting their growth. This study explores the solid-state fermentation of wheat and corn bran using three fungal species: Pleurotus ostreatus, Fomes fomentarius and Ganoderma lucidum. Both brans are fiber-rich, with starch and arabinoxylans as their main components. However, corn bran contains more total carbohydrates and a higher concentration of phenolic compounds. The changes in the compositional profile and structure of the substrates were followed during the fermentation process. To elucidate fungal degradation strategies, we monitored enzymes activities over 14 days of fermentation, focusing on those responsible for the breakdown of amylose, arabinoxylans, β-glucans, cellulose, and lignin. Fourier transform infrared spectroscopy (FT-IR) revealed a significant reduction of the polysaccharides and lignin acetyl groups, alongside an increase in the absorbance of the protein- and chitin-related signals. These findings aligned with scanning electron microscopy (SEM) images, which revealed structural changes in the brans. The formation of mycelium reinforced and interconnected the lignocellulosic fibers, allowing for a preliminary assessment of the characteristics of the resulting composite material. Overall, this study provides key insights into how these fungal species degrade cereal-based materials, linking substrate composition to enzymatic activity and highlighting their potential for bio-composite applications.