The use of chitosan in diverse areas is directly related to the polymer's molecular weight and degree of deacetylation, which depends on the conditions of chitin deacetylation. The aim of the present study consisted of optimization of the deacetylation stage in the production of chitosan, using the response surface methodology for the polymer's molecular weight. Chitin was obtained from shrimp wastes and the study of deacetylation made through a factorial experimental design, where temperature and time were varied. The estimate of chitosan's intrinsic viscosity was made by linear regression with the values of reduced viscosity and concentration, using Huggins equation for polymers. The viscosity average molecular weight of chitosan was calculated for each experiment by the equation by Mark-Houwink-Sakurada that relates the intrinsic viscosity to the polymer's molecular weight. The optimum condition for the deacetylation reaction for molecular weight was observed at a temperature of 130 degrees C and in 90 min, and corresponded to a molecular weight of chitosan of about 150 kDa, and a deacetylation degree of 90%. (c) 2006 Elsevier Ltd. All rights reserved.