We previously studied the effects of 2-100 kGy gamma radiation (generated from (60) Co) on physicochemical, thermal, morphological, and antimicrobial properties of chitosan. The results demonstrated that these properties of chitosan were largely influenced by the action of gamma radiation. In addition, the fat binding capacity (FBC) of chitosan was found to be increased with increasing irradiation doses. In this work a thorough in-vivo investigation on mice was performed to examine FBC of irradiated chitosan (30-100 kGy) in animal bodies. Different groups of mice specimens were fed with gamma-irradiated chitosan along with natural rodent chow and cheese as well as sufficient supply of water. The unconsumed lipid measured in feces was found to increase by 67% in mice whose diet included 100 kGy irradiated chitosan, relative to that nonirradiated chitosan. After twelve weeks of intimate observation, mice were sacrificed to examine triglyceride (TG) and total cholesterol (TC) content in mice blood. The results demonstrated that TG and TC values of mice fed with gamma-irradiated chitosan were significantly lower than that of the control. All of these findings are expected to enhance the future research on irradiated chitosan to be used as potential fat reducer in human metabolism.