This study presents a new approach for direct carboxyalkylation of chitosan in the gel state by using aza-Michael addition and substitution reactions. Various reagents were applied including acrylic and crotonic acids, and α-, β-, γ-, δ-, and ɛ-halocarboxylic acids. The reaction of chitosan with γ- and δ-halocarboxylic acids showed no target product formation either in solution or in the gel state. In the case of acrylic, crotonic, α- and β-halocarboxylic acids, the reaction performed in the gel state (concentration of chitosan 20–40%) shows higher degree of substitution at lower reaction time and temperature than in diluted solutions (concentration of chitosan 0.5–2%). The results were discussed in terms of kinetics of the target and side reactions. 1 H and 13 C NMR confirmed that in all cases the carboxyalkylation of chitosan proceeds exclusively at the amino groups.