Abstract: Carboxymethyl-chitosan (OCMC) with high water solubilities was obtained by carboxymethylation of chitosan. It has good stability and antibacterial property. Comparing the solubility of OCMC dissolving in difference solvents, it is found that the best solvent condition of OCMC is 2wt% acetic acid aqueous. The Ag-OCMC composite particles were obtained by complex of OCMC and Ag nanoparticles (AgNPs). The composition, microstructure and thermal properties of Ag-OCMC composite particles were characterized by UV-Vis, FTIR, XPS, TEM, SEM and TG-DTA. Antimicrobial activities of Ag-OCMC composite particles were performed by using typical bacteria of E.coli and S.aureus. The results show that AgNPs are face-centered cubic crystallites with the average diameter size in 40-50 nm. The decomposition temperatures of chitosan and OCMC are raised by the introduction of AgNPs. The antibacterial activity of Ag-OCMC composite particles is significantly higher than single chitosan based antibacterials.