BACKGROUND: The application of deacetylated chitin (chitosan, DC) prepared by traditional technique was limited because of its lower degree of deacetylation, impurity and relative lower molecular mass.OBJECTIVE: To improve the traditional technique for extraction and preparation of DC from the rustae f oratosquila oratoria.DESIGN: Contrasting observation.SETTING: Shandong Institute of Biopharmaceutics.MATERIALS: The experiment was carried out in the Shandong Key Laboratory for iopharmaceutics, Shandong Institute of Biopharmaceutics from February 2003 to January 2004. Experimental nstrument: Mettler AE240 electronic analytical balance and ZK-40AB electrothermal vacuum drying oven were rovided by Mettler-Toledo Instruments Co., Ltd. And ShangHai Shuli Instruments Co.,Ltd., respectively. Xperimental materials: oratosquila oratoria was purchased from Jinan aquatic products market.METHODS: ①C as traditionally prepared from chitin by decoloring with strong oxidant and deacetylating with concentrated alkaline liquor under high temperature. Chitin was extracted from crustae of shrimp and crab fter decalcification with diluted acid and deproteinization with diluted base. ②The improved preparation echnique: The crustae of oratosquila oratoria was decalcificated and decolorized with diluted acid, and as deproteinized and decolorized with diluted base at room temperature, and then the chitin was obtained fter the second decalcification and decolorization with diluted acid. The crude DC was obtained from hitin after deacetylation and decolorization with concentrated ase at 55-65 ℃. The crude DC was issolved n diluted acid and filtered. The filtrate was collected, precipitated with dilute base. After filtering, he sediments were retained, washed with water and dried. Then pure DC was obtained.MAIN OUTCOME MEASURES: he comparison between improved technique and traditional technique; Color, dissolvability in diluted cid, ield, degree of deacetylation and dynamic viscosity of DC prepared by different techniques.RESULTS: ①echnique comparison: Compared with traditional technique, the reaction of improved preparation technique as milder, and the deproteinization was at room temperature; it did not need an isolated decolorization;deacetylation was at low temperature, and had a refine process. ②Detection indexes of DC: he yield of DC prepared by improved technique was little lower than that by traditional technique (15%, 7% respectively). The degree of deacetylation and dynamic viscosity were both higher than those by raditional technique (＞ 95%,＜ 70%; ＞ 120mPa·s,＜ 80 mPa·s , respectively). The color was white or lmost white, which was better than that by traditional technique (yellow or gray). The DC could ompletely issolve in dilute acid, and the dissolvability was better than that by traditional technique (dissolved artly in dilute acid).CONCLUSION: Compared with the traditional technique, the improved technique was mpler and the reaction conditions were milder. And also the quality of obtained DC was obviously improved.