Biomaterials such as nanocrystalline cellulose (NCC) have attracted considerable attention in coating production industries due to their sustainable and renewable attributes. This work presents NCC obtained from the hydrolysis of microcrystalline cellulose and sulfation treatment of NCC to obtain sulfated-NCC (S-NCC) using a chemical agent for corrosion protection of mild steel in 3.5 wt.% NaCl solution. Two types of anticorrosion coatings were formulated by incorporating either NCC or S-NCC of different loading ratios (10 wt.% to 50 wt.%) to epoxy-matrix to form composite coatings. The structural characterisations of NCC and S-NCC showed that the sulfation introduced sulfate ester groups on NCC. The morphological characterisations displayed that the average particle sizes obtained for both ranged between 40 nm and 50 nm. Electrochemical measurements were conducted to obtain the anticorrosion behaviour of the composite coatings in the corrosive solution. The results indicated that the sulfation of NCC improved the anticorrosion performance to 99.7%, and the best performance was obtained from a coating containing 20 wt.% S-NCC. Finally, a mechanism for corrosion protection of S-NCC coating was proposed where electrostatic repulsion of chloride species from the coated mild steel occurred. This study, therefore, demonstrates the applicability and importance of S-NCC in improving the anticorrosion performance of epoxy coatings for maritime applications.