Abstract: Chitosan, the N-deacetylation product of chitin has been applied in many fields, due to its biocompatible and biodegradable properties as well as its relative ease to manage compared to its chemical precursor. The control of their chemical and physical properties allows Chitosan derivatives to be used for different biomedical and industrial applications. Degree of deacetylation (DD) and polymer chain length (molecular weight, Mw) can be considered the most important features to determine the physico-chemical properties of these systems and consequently decisive factors to give desired results in formulations and applications.  On the other hand, ureide compounds have been employed in different applications fields such as catalysis involving the selective synthesis of tertiary thiols or medicinal chemistry as glutathione analog. We report here, the synthesis in water of new ureidyl chitosan derivatives and their characterization by NMR techniques both in solution and solid state. Aliphatic and aromatic diisocyanates were used as crosslinking agents to obtain a chitosan network with potential physicochemical properties in gel formation. We thank the AECID (Projects A/023577/09 and A/030422/10) and the 'Junta de Andalucía' (FQM 142 and Project P09-AGR-4597) for financial support.