Paperboard mill results in the production of huge quantity of solid waste material, namely, the sludge. The volume and its high moisture content makes sludge difficult to handle, transport or store for a long duration. This paper has characterized the generated paperboard mill sludge and further used for synthesis of nanocellulose using 90% citric acid solution at 80OC for a duration of 4 hours. The synthesized nanocellulose had a width of 13–25 nm and length of 450–490 nm, with a ζ-potential value of -29.5 mV. When compared to a commercially available microcrystalline cellulose sample, the thermal analysis exhibited better observation.