Human organic anion transporters hOAT1/SLC22A6 and hOAT3/SLC22A8 are highly expressed on the basolateral membrane of renal proximal tubules and mediate tubular uptake of anionic drugs from blood. They play an important role for drug disposition, and therefore close studies of their ligand recognition are important for drug therapy and development. In this study, we performed uptake experiments using HEK293 and fluorescent anion 6-carboxyfluorescein to asses the effects of phenylpropanoids on hOAT1 and hOAT3. We found that phenylpropanoids, 3-(4 '-isopentenyloxyphenyl)-benzoic acid (IBA), 3-(4 '-isopentenyloxy-3 '-methoxyphenyl)-benzoic acid (IMBA), and 3-(4 '-geranyloxy-3 '-methoxy phenyl)-benzoic acid (GMBA) inhibited hOAT1 and hOAT3. The K-i values for hOAT1 were comparable to that of probenecid, a strong inhibitor of hOAT1 and hOAT3. While IBA demonstrated competitive inhibition, IMBA and GMBA showed mixed-type inhibition. After preincubation and washout, the inhibitory effects remained with IMBA and GMBA but not IBA, suggesting that the functional group at 3'-position is responsible for these differences. In conclusion, IBA, IMBA, and GMBA are inhibitors of hOAT1 and hOAT3. (C) 2017 Elsevier Inc. All rights reserved.