Aims: Phloridzin, a glucoside of the flavonoid-like polyphenol phloretin, has long been known to be a specific nontransportable inhibitor of the human sodium-dependent glucose transporter hSGLT1. To identify further hypoglycemic agents from plants, we investigated the effect of some extracts (mixtures of different flavonol glycosides, phenolic acids and anthocyanidines) derived from green cabbage and grape seeds on the hSGLT1 response. Methods: Therefore, this transporter was expressed in Xenopus oocytes by injecting, and the current response evoked by 1-O-methyl-alpha-D-glucopyranoside (aMDG), a non-metabolizable analogue of glucose, was measured by the two electrode voltage clamp method. Results: 9 out of the 17 extracts investigated showed an inhibitory effect of at least 20% on the current induced by 1 mM aMDG. Another 6 extracts were transported themselves by inducing a current of at least 40% of the current induced by aMDG. One of the grape seed extracts inhibited the aMDG induced current by as much as 76.6% (±4.1%, n=5), and the current could not be restored even after 30 minutes of washing out. Further investigation of the effects of this extract on other electrogenic transporters revealed that the irreversible effect seen in hSGLT1 was also observed on the human peptide transporter hPEPT1 as well as on the mouse proton-coupled amino acid transporter mPAT1. The current induced by 1 mM glycylsarcosin in hPEPT1-expressing oocytes was inhibited by 84.1% (±2.6%, n=5) and the current induced by 5 mM glycin in mPAT1 by 83.1% (±1.7, n=5). The inhibitory effect of this extract was also present in the nominal absence of extracellular Ca²⁺. Conclusion: Inhibition of hSGLT1 by 9 extracts isolated from either green cabbage or grape seeds suggests the presence of possible hypoglycemic agents in these plants, but purification and identification of their constituents will be necessary to clarify their exact properties.