Human organic anion transporters (hOATs) play critical roles in the body disposition of clinically important drugs. Understanding the regulation of hOATs has profound clinical significance. My thesis work focuses on delineating molecular and cellular mechanisms underlying hOAT regulation, and consists of three parts. In the first part, we examined the regulation of hOAT trafficking and function by ubiquitination through cell signaling pathways (protein kinase C, protein kinase A, and their upstream hormones AngII and bradykinin) by combined approaches of cellular biology, site-directed mutagenesis and mass spectroscopy. We identified PKC isoforms involved in OAT regulation. We also identified lysine residues serving as ubiquitin-conjugating sites. In the second part, we examined transporter-mediated drug-drug interactions by screening two prescription drug libraries against hOAT1 and hOAT3. High potent inhibitors were identified. Computational analyses reveal several important properties which differentiate between inhibitors and non-inhibitors. Such model provides mechanistic insights for predicting new OAT inhibitors. In the third part, we studied structure and function relationship of hOATs. Critical transmembrane domain and amino acid residues were identified, which play important role in OAT stability, maturation efficiency as well as ologomerization.