The role of Ca²⁺ activated Cl^- channels (CaCC) for renal function is unknown. By immunohistochemistry we demonstrate expression of the recently identified CaCC, Anoctamin 1 (Ano1, TMEM16A), in human and mouse podocytes and proximal tubular epithelial cells. Ano1 null mice demonstrate proteinuria and show a large number of big reabsorption vesicles in proximal tubular epithelial cells. Selective knockout of Ano1-expression in mouse podocytes (Ano1^-/-/Cre^Nphs2) did not impair renal function, whereas tubular knockout in Ano1^-/-/Cre^Ksp mice increased and decreased urine protein and electrolyte concentrations, respectively. Purinergic stimulation activated Ca²⁺ dependent Cl^- currents in isolated proximal tubular epithelial cells from Ano^+/+ animals, but not in cells from Ano1^-/-/Cre^Ksp mice. Moreover, Ano1 currents were activated by acidic pH, suggesting parallel stimulation of Ano1 Cl^- secretion with activation of the H⁺-ATPase. Lack of Ca²⁺ dependent Cl^- secretion in cells from Ano1^-/-/Cre^Ksp mice was paralleled by attenuated H⁺ secretion by the H⁺-ATPase, and by reduced endosomal acidification, which compromised proximal tubular albumin uptake. Reduced proximal tubular Cl^- secretion was compensated by enhanced serum renin and aldosterone concentrations, leading to enhanced distal tubular reabsorption, thus maintaining normal blood pressure levels. These results establish a role of Ano1 for proximal tubular H⁺ secretion and protein reabsorption.