The hydrolysis of cellulose to high-yield glucose in water remains challenging owing to the limited acidity and substrate contact of sulfonated carbons. Herein, we report a unique sulfonated mesoporous carbon fiber with optimized acidity prepared by the pyrolysis of FeCl₃-impregnated wipe fibers followed by acid treatment. The Brønsted acidity (especially for SO₃H) was produced by sulfonation of the magnetic carbon fiber intermediate, while Lewis acidity originated from small Fe₃O₄ nanoparticles and the remaining defects. The balanced Brønsted and Lewis acidity combined with hydrophilic functionalities was simultaneously tailored by varying the Fe/wipe fiber (WF) feed ratio and pyrolysis temperature to change the porous structure of the final catalysts. The elaborately fabricated MCF-SO₃H-20-500 (20% Fe/WF feed ratio and pyrolysis at 500 °C) delivered 66.0% glucose yield as cellulose was completely converted. This is the highest glucose yield achieved by the hydrolysis of untreated cellulose in water over a sulfonated carbon catalyst. The optimized Brønsted and Lewis acidity was mainly responsible for the controlled conversion of cellulose to glucose, while the rich hydrophilic functionalities and superior mesoporous structure of the catalyst facilitated contact to cellulose and mass transfer. This investigation will open new avenues to design high-performance carbon sulfoacid catalysts toward cellulose hydrolysis.