This study proposes the utilization of mango peel residues from the Kent variety (Mangifera indica), generated by agro-industrial processes in Northern Peru (approximately 3,840 tons/year), for the production of cellulose nanofibrils (CNF), offering a value-added alternative for waste generated by agro-industries. The main objective was to determine the optimal CNF yield under two temperature levels: reaction time and sulfuric acid concentration. The raw material underwent the following pretreatment steps: immersion washing in water at 90 °C for 20 minutes, followed by drying and sieving. Subsequently, it was washed with 96% ethanol through steam stripping. An alkaline treatment with 8% NaOH was applied at a solid-to-liquid ratio of 1:15 at 75–80 °C for 4 hours with constant stirring at 500 rpm. For the bleaching stage, the fibers were treated with an equal-part solution of acetate buffer and aqueous sodium chlorite at 80 °C for 6 hours under continuous agitation. Afterward, a mechanical treatment was applied, followed by acid hydrolysis using sulfuric acid at varying concentrations (2%, 6%, 10%) with a 1:20 solid-to-liquid ratio, reaction times of 60 and 90 minutes, and temperatures of 60 °C and 80 °C. The resulting suspension underwent sonication in an ultrasonic bath (300 W) over ice for 30 minutes. The mixture was then subjected to successive washes with distilled water for dialysis, using dialysis membranes with a molecular weight cut-off of 12–14 kDa. Finally, the suspension was freeze-dried and sonicated again at –45 °C to obtain CNF particles. The resulting nanocellulose yields ranged from 86% to 99% (dry CNF weight/cellulose weight) and 18.35% yield based on dry residue weight (dry CNF weight/initial raw mass weight). The most efficient condition was achieved at 80 °C, 2% H₂SO₄, and 60 minutes of reaction time. This chemo-mechanical process represents a sustainable and low-cost alternative for biomaterial production from agro-industrial waste, contributing to environmental impact reduction.