A convenient and rapid method is described for the synthesis of nitrogen heterocyclic derivatives by one-pot three-component reaction of substituted aromatic aldehydes, dicarbonyl- and 2-aminobenzothiazole/3-amino-1,2,4-triazole/urea/thiourea using commercially available chitosan in 2% acetic acid in aqueous media at 60-65 degrees C. Chitosan was used as an efficient biodegradable and reusable green catalyst for this multicomponent reaction. The chitosan catalyst can be reused 10 times in fresh reaction. Catalytic activity has been sustained in the first five runs but slightly decreased in subsequent cycles.