The objective of the study is to elucidate the effect of reaction time and temperature during heterogenous alkali reaction on degree of deacetylation (DD) and molecular weight (MW) of the resulting chitosans, and to establish the reaction conditions to obtain desired DD and MW chitosan products. Chitin was extracted from red shrimp process waste. DDs and MWs were determined by infrared spectroscopy (IR) and static light scattering, respectively. The results are as follow: The DD and MW of chitin obtained were 31.9% and 5637 kDa, respectively. The DD of the resulting chitosan increased along with reaction time and/or reaction temperature. The DDs of the resulting chitosan that were obtained from 140degreesC were higher than those reacted at 99degreesC. The highest DD of the resulting chitosans after alkali deacetylation at 99 and 140degreesC were 92.2 and 95.1%, respectively. The DDs of chitosans increased fast at the beginning of reaction process then slowed over time. The reaction rate and rate constant of the deacetylation reaction decreased with increasing DD of the reactant. The MWs of chitosans decreased along with the deacetylation time. MW of those chitosans reacted at 140degreesC are smaller than those at 99degreesC. The rate of chitosan degradation was above 43.6%/h in the initial stage, then decreased to about 20%/h. The degradation rate constants raised substantially in the late stage. (C) 2003 Wiley Periodicals, Inc.