The aim of this study was to evaluate the anti-prediabetic effect of 6-O-caffeoylsophorose (CS) isolated from red vinegar in prediabetic spontaneously diabetic Torii (SDT) rats. The effect of CS on glucose uptake in rat skeletal muscle L6 myotubes was also investigated. By the supplementation of CS at a dose of 100 mg/kg/day for 8 weeks to 8-week-old SDT rats, impaired glucose tolerance in 12- and 16-week-old rats was improved in CS group, along with promoted insulin secretion. In a glucose uptake study using 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]- 2-deoxyglucose (2-NBDG), > 50 μM CS stimulated uptake of 2-NBDG and translocation of glucose transporter 4 (GLUT4) to the plasma membrane. In CS-treated L6 cells, western blot analysis showed phosphorylation of AMPactivated protein kinase (AMPK) but not of Akt. Consequently, we concluded that CS showed an in vivo antiprediabetic effect, and promoted GLUT4 translocation in L6 myotubes possibly through the activation of the AMPK signaling pathway.