Gestational potassium retention, most of which occurs during late pregnancy, is essential for fetal development. The purpose of this study was to examine mechanisms underlying changes in potassium handling by the kidney and colon in pregnancy. We found that potassium intake and renal excretion increased in late pregnancy while fecal potassium excretion remained unchanged and that pregnant rats exhibited net potassium retention. By qPCR we found markedly increased H+/K+-ATPase type2 (HKA2) mRNA expression in cortex and OM of late pregnant vs virgin. ROMK mRNA was unchanged in the cortex, but apical ROMK abundance (by immunofluorescence) was decreased in pregnant vs virgin in the distal convoluted tubule (DCT) and connecting tubule (CNT). BKa protein abundance in intercalated cells in cortex and outer medullary collecting ducts (by immunohistochemistry) fell in late pregnancy. In the distal colon we found increased HKA2 mRNA and protein abundance (western blot) and decreased BKα protein with no observed changes in mRNA. Therefore, the potassium retention of pregnancy is likely to be due to increased collecting duct potassium reabsorption (via increased HKA2) and decreased potassium secretion in (via decreased ROMK and BK), as well as increased colonic reabsorption via HKA2.