Damage to endothelial cells contributes to acute kidney injury (AKI) by leading to impaired perfusion. Endothelial colony-forming cells (ECFCs) are endothelial precursor cells with high proliferative capacity, pro-angiogenic activity, and in vivo vessel forming potential. We hypothesized that ECFCs may ameliorate the degree of AKI and/or promote repair of the renal vasculature following ischemia/reperfusion (I/R). Rat pulmonary microvascular ECs (PMVEC) with high proliferative potential were compared with pulmonary artery ECs (PAEC) with low proliferative potential in rats subjected to renal I/R. PMVEC administration reduced renal injury and hastened recovery as indicated by serum creatinine and tubular injury scores, while PAEC did not. Vehicle-treated control animals showed consistent reductions in renal medullary blood flow (MBF) within 2 hours of reperfusion, while PMVEC protected against loss in MBF as measured by laser Doppler. Interestingly, PMVEC mediated protection occurred in the absence of homing to the kidney. Conditioned medium (CM) from human cultured cord blood ECFC also conveyed beneficial effects against I/R injury and loss of MBF. Moreover, ECFC-CM significantly reduced the expression of adhesion molecules such as ICAM-1 and p-selectin, and decreased the number of differentiated lymphocytes typically recruited into the kidney following renal ischemia. Taken together, these data suggest that ECFC secrete factors that preserve renal function post ischemia, in part, by preserving microvascular function.