•Cellulose depolymerization using an ionic liquid as solvent and a solid catalyst.•Cellulose depolymerizes via a second order reaction under optimized conditions.•Optimized depolymerization enables precise control of cello-oligomer chain lengths. Cellulose extracted from printed paper wastes were selectively depolymerized under controlled conditions into cello-oligomers of controllable chain lengths via dissolution in an ionic liquid, 1-allyl-3-methylimidazolium chloride (AMIMCl), and in the presence of an acid catalyst, Amberlyst 15DRY. The depolymerization process was optimized against reaction temperature, concentration of acid catalyst, and reaction time. Despite rapid initial depolymerization process, the rate of cellulose depolymerization slowed down gradually upon prolonged reaction time, with 75.0wt% yield of regenerated cello-oligomers (mean Viscosimetric Degree of Polymerization value of 81) obtained after 40min. The depolymerization of cellulose fibers at 80°C appeared to proceed via a second-order kinetic reaction with respect to the catalyst concentration of 0.23mmol H3O+. As such, the cellulose depolymerization process could afford some degree of control on the degree of polymerization or chain lengths of cello-oligomers formed.