The mixture solutions of glucosamine and chitosan with different molecular weights (123.5; 40.7 and 6.1 kDa) were irradiated by Co-60 gamma ray at dose of 50 kGy to prepare chitosanglucosamine Maillard reaction products (MRPs). The formation of MRPs was determined by measuring UV absorbance (at 284) nm and browning (at 420 nm). The reaction efficiency was calculated based on the ratio of reacted glucosamine and total added glucosamine. The antibacterial activity of chitosan-glucosamine MRPs against Escherichia coli was also investigated. The obtained results showed that the chitosan-glucosamine MRPs exhibited strong antibacterial activity, in which chitosan-glucosamine MRPs prepared from 123.5 kDa chitosan could reduce up to 4 log CFU/ml in comparison with the control (45 × 106 CFU/ml). Therefore, the chitosan-glucosamine MRPs prepared by the Co-60 gamma irradiation method can be potentially applied as a natural preservative for food, cosmetics and substituted for banned chemical preservatives.