Slc26a6 (PAT-1), a multi anion transporter, is strongly expressed in the apical membrane of the upper small intestine, where it is colocalized with another member of the same gene family, Slc26a3 (DRA) This study investigates the role of PAT-1 in electrolyte and fluid absorption under the unique ionic conditions of the upper GI tract. Small intestinal fluid absorption was assessed by single pass perfusion of solutions with different ionic compositions through jejunal segments of anesthetized mice, and assessment of volume and pH of the inflowing and outflowing solutions.. WT jejunum absorbed fluid and acidified the luminal perfusate. DRA-deficient jejunum absorbed less fluid than WT, and acidified the lumen more strongly, consistent with its action as a Cl^-/HCO₃^- exchanger. PAT-1-deficient jejunum also absorbed less fluid, but resulted in less luminal acidification. Switching the luminal solution to a 5% CO₂/HCO₃^- buffer, pH 7.4, resulted in decrease in jejunal enterocyte pH_i, measured by two photon confocal microscopy in exteriorized, vascularly perfused jejunum, and strongly augmented fluid absorption in a PAT-1- and Na⁺/H⁺ exchanger 3 (NHE3)- but not DRA-dependent manner. Even in the absence of luminal Cl^-, luminal CO₂/HCO₃^- was able to augment fluid absorption in WT and DRA-deficient, but not in PAT-1- and NHE3-deficient mice, indicating that PAT-1 likely serves to import HCO₃^- under these circumstances. The results suggest that PAT-1 plays an important role in jejunal Na⁺HCO₃ ^- reabsorption, thus contributing significantly to intestinal fluid absorption and systemic acid/base balance.