Chemical reactivity of beta-chitin isolated from squid pens has been examined in various reactions to elucidate the possibility of facile modifications in simple manners leading to the preparation of derivatives with well-defined structures. beta-Chitin swelled in common solvents such as methanol and pyridine unlike the ordinary alpha-chitin and exhibited much higher reactivity than alpha-chitin. Free amino groups present in beta-chitin were easily and selectively acetylated with acetic anhydride in methanol to give chitin with a uniform structure, poly(N-acetyl-D-glucosamine). When acetylation reaction was carried out in pyridine, O-acetylation proceeded smoothly besides N-acetylation. In the presence of 4-dimethylaminopyridine as the catalyst, even full acetylation was achieved under mild conditions. Tosylation was also quite efficient in pyridine without side reactions such as N-deacetylation which is unavoidable in the tosylation of alpha-chitin. beta-Chitin also enabled direct tritylation in pyridine in the presence of 4-dimethylaminopyridine. All these reactions were quite sluggish with alpha-chitin, and no reactions or only very low extents of substitution were observed, indicating the high potential of beta-chitin as a versatile starting material for facile modification reactions.