In this paper we study the extraction-purification process of both chitin and chisotan from mollusk shells. Our aim is to optimize the method for the polymers production with high molecular weight and a high degree of acetylation (DA) for chitin, and a low DA for chitosan. A demineralization with HCl solution was carried out, and afterwards a deproteinization and deacetylation using NaOH aqueous solution. Different times, temperatures and concentration of reagents were analyzed. From the study of the deproteinization of chitin it was found that the process time has little effect on chitin-chitosan yield, and that no clear tendency for chitosan DA can be observed. However, a higher temperature in the deproteination of chitin leads to a higher yield and chitosan DA. This would suggest that shorter times and higher temperatures in the deproteinization of chitin provide better conditions to reach chitosan with low DA.