Antibacterial activity of high molecular weight water-soluble (HMWWS) chitosan (800 kDa) was investigated against four Gram-negative (Escherichia coli, Salmonella typhimurium, Vibrio cholerae and Vibrio parahaemolyticus) and two Gram-positive (Staphylococcus aureus and Listeria monocytogenes) bacteria. Catfish fillets were surface-inoculated with these food-borne pathogens and coated with chitosan dissolved in aspartic acid (AS) or acetic acid (AC) solution at different concentrations (1% or 3%). Samples were stored at 4 degrees C for 8 days, except for those inoculated with Vibrio species (10 degrees C for 6 days). Overall, the most effective coating treatment was the 3% HMWWS chitosan in AS solution (800AS3%). Compared with the control, significant (P < 0.05) reductions caused by 800AS3% were observed for all tested pathogens at the end of storage. The growth of V. parahaemolyticus was completely suppressed by 800AS3%. This study demonstrated that HMWWS chitosan in AS solution could be used as an alternative antimicrobial coating for catfish fillets.