A process for producing chitin nanocrystals (ChNCs) involves contacting a chitinous material with a sufficient amount of an inorganic persulfate to produce chitin nanocrystals from the chitinous material. The process permits one-spot production of ChNCs from biomasses such as crustaceans, fungi, mushrooms, insects or mixtures thereof. Chitin nanocrystals produced by the process comprise surface carboxylic groups and are not initially deacetylated.