ABSTRACT: People in oriental countries, including Japan and Taiwan, boil guava leaves (Psidium guajava L.) in water and drink the extract as a folk medicine for diabetes. The present study investigated the enhancement of aqueous guava leaf extract on glucose uptake in rat clone 9 hepatocytes and searched for the active compound. The extract was eluted with MeOH-H2O solutions through Diaion, Sephadex, and MCI-gel columns to separate into fractions with different polarities. The uptake test of 2-[1-14C] deoxy-D-glucose in rat clone 9 hepatocytes was performed to evaluate the hypoglycemic effect of these fractions. The active compound was identified by nuclear magnetic resonance analysis and high-performance liquid chromatography (HPLC). The results revealed that phenolics are the principal component of the extract, that high polarity fractions of the guava leaf extract are enhancers to glucose uptake in rat clone 9 hepatocytes, and that quercetin is the major active compound. We suggest that quercetin in the aqueous extract of guava leaves promotes glucose uptake in liver cells, and contributes to the alleviation of hypoglycemia in diabetes as a consequence.