The aim of this study is to elucidate the antibacterial activity of medium molecular weight chitosan (MMWC) along with keeping antioxidant activity of Moringa oleifera leaves extracts, which has shown the significant antioxidant activity. Antioxidant activity of the extracts as either free or ingredient in edible food was investigated in vitro by radical scavenging assays with 2,2-Diphenyl-1-picrylhydrazyl (DPPH), 2,2’-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and 2,4,6-Tris(2-pyridyl)-s-triazine (FRAP). The results showed that extracts has showed high antioxidant activity while added in edible food as like a muk, although when it was added in muk as food additives, its original activity was reduced slightly. In addition, in the presence of MMWC with ranging from 3 to 8-kDa in muk, various improvements including antibacterial effect and stability of structure of muk were observed. Taken together, specified size of chitosan seems to be a good candidate playing a key role to maintain the antioxidant and antibacterial activities in functional foods.