Lignocellulosic recyclable packaging material is in high demand, because of the emergence of e-commerce. Old corrugated container (OCC) pulp is the main raw material in China for manufacturing packaging boxes/bags, but its strength needs improvement. In this project, waste cellulose in the form of used printing paper was oxidized using 2,2,6,6-tetramethylpiperidine-l-oxyl radical (TEMPO) concept so that more carboxyl groups were introduced. The TEMPO-oxidized waste cellulose (TOWC) having a carboxyl content of 1.451 mmol/g was then used as reinforcement for the OCC fiber networks. The TOWC addition to the OCC fiber networks at different mass ratios of 5%, 10%, and 15% on its strength properties was studied. The results showed that the addition of TOWC remarkably improved the tensile and other strength properties, which can be explained by the improved hydrogen bonding and interpenetrating capacity of fiber networks, thanks to the increased carboxyl groups and fibrillation after the TEMPO oxidation.