In order to expand the scope of protection of the amino group of chitosan for synthesizing a key intermediate that would allow regioselective modification reactions, dichlorophthaloylation behavior was studied in detail. The reaction proceeded in a similar manner to phthaloylation, and chemoselectively protected N-dichlorophthaloyl-chitosan could be prepared either by partial hydrolysis of N,O-dichlorophthaloylated chitosan or by one-step dichlorophthaloylation in N,N-dimethylformamide/water. Deprotection of N-dichlorophthaloyl-chitosan was achieved by hydrazinolysis followed by alkaline hydrolysis. GPC measurements revealed that the number-average molecular weight was reduced to about a half after the protection-deprotection process, indicating the cleavage of the main chain to be not pronounced. In the triphenylmethylation, N-dichlorophthaloyl-chitosan exhibited adequate reactivity for facile protection of the C6 hydroxy group. The dichlorophthaloyl group has thus proved to be a promising candidate to prepare a novel precursor for controlled chemical modifications of chitosan.