beta-Chitin was extracted from squid pens and its heterogeneous alkaline deacetylation was performed under various conditions. The kinetics of the first, second and third deacetylation reaction of beta-chitin was investigated under conditions minimizing bulk mass transfer. It was found that the effects of temperature and reaction time on the first, second and third deacetylation of beta-chitin were similar. A shrinking core model of a sphere with surface reaction is proposed to describe the deacetylation reaction of beta-chitin. The experimental data fit the theoretical model very well. The controlling step of the reaction changes from the chemical reaction to diffusion through an ash layer with increase in temperature and time of deacetylation. The phenomenon of stagnation is mainly caused by the structure of beta-chitin.