The aim of this study was to evaluate the quality properties of tuna extract with the addition of active molecular chitosan (AMC) derived from the partial digestion of high molecular weight chitosan (CTSN-H). Various chitosans such as high molecular weight chitosan (CTSN-H), chito-oligosaccharides (COS) and active molecular chitosan (AMC) were used to evaluate the potent additives in the tuna extract. Amongst several series of chitosan, we found that addition of AMC into tuna extract resulted in the significant saving effect of antioxidant activity of its tuna extract, without changing of color and making any insoluble or unmixed forms. Especially, AMC derived from the partial degradation of CTSN-H which was dissolved in 1% acetic acid with apple-skins for three weeks showed highly recommendable antimicrobial activity against Penicillium italicum. These results demonstrated that solvent dependent solubility may effect on the antimicrobial activity of chitosan, possibly can be used for other extracts that have been used for functional drinks.