Pineapple peel was used to make cellulose nanocrystals. The peel was cleaned and bleached to remove impurities. The process resulted in purified cellulose with high purity. Nanocrystals were extracted from the cellulose, showing small sizes and negative charges. Longer bleaching time was more effective. Pineapple peel is a good source of cellulose for making nanocrystals.