Wood cellulose was converted to individual nanofibers of approximately 4 nm width and 380-570 nm average length by TEMPO-mediated oxidation. The TEMPO-oxidized cellulose nanofibers (TOCNs) were orally administered with glucose and glyceryl trioleate to mice and postprandial responses of blood glucose, insulin, glucose-dependent insulinotropic polypeptide (GIP), and triglycerides were studied. Both blood insulin and GIP concentrations were decreased by TOCN with: aCarboxyl content and aspect ratio of 1.2 mmol g(-1) and 120, respectively, in dose-dependent manners (0-0.3mg g(-1) body weight). Of the TOCNs examined, that with a carboxyl content and aspect ratio of 1:2 mmol g(-1) and 120, respestively, was the most effective in reducing postprandial blood glucose, plasma insulin, GIP, and triglycericie concentrations. Thus, TOCNs were found to exhibit characteristic biological activities when administered to mice and may have potential applications in biomedical fields for human health.