Aims: Glycogen synthase kinase 3 GSK3b participates in the regulation of metabolism, migration and cell proliferation. As it is expressed in epithelial tissues, the possibility was considered that it contributes to the regulation of epithelial transport. The present study thus explored whether GSK3b influences amino acid transport. Methods: The amino acid transporter SN1 (SLC38A3) was expressed in Xenopus oocytes with or without GSK3b and amino acid-induced current (Ig) determined by dual electrode voltage clamp. To explore whether GSK3b sensitivity of SGLT1 participates in the regulation of electrogenic intestinal amino acid transport, Ussing chamber experiments were performed in intestinal segments of gene-targeted knockin mice expressing mutated and thus PKB/SGK-resistant and disinhibited GSK3a,b (gsk3^KI), in which the serines of the PKB/SGK phosphorylation sites had been replaced by alanine. The gsk3^KI mice were compared to matching wild type mice (gsk3^WT). Results: In Xenopus oocytes expressing SN1, but not in water-injected oocytes addition of 5 mM glutamine induced an inwardly-directed Ig, which was significantly enhanced by coexpression of GSK3b. In intestinal segments from gsk3^KI mice, the current induced by phenylalanine, methionine, glutamine and proline was significantly larger than in gsk3^WT mice. Moreover, the urinary excretion of glycine, alanine, proline and valine tended to be smaller in gsk3^KI than in gsk3^WT mice. Conclusion: The present observations reveal a role of GSK3b in the regulation of epithelial amino acid transport.