Urea transporters (UTs) are transmembrane urea-selective channel proteins that include two UT subfamilies, UT-A and UT-B. UT-A subfamily includes six members, UT-A1 to UT-A6, which are mainly expressed in kidney. UT-B subfamily has only one member that has a wide distribution in the body. UTs have been confirmed to play important roles in urinary concentration via the phenotypic analysis of 6 UT selective knockout mouse models. Experimental results suggest that UTs might be diuretic targets and that UT inhibitors might be developed as novel diuretics. This article reviews the physiological function and drug discovery of UT.