Disclosed herein is an integrated reservoir tank assembly for a vehicle. The integrated reservoir tank assembly for a vehicle includes an integrated reservoir tank in which an inner space is partitioned into a first chamber configured to store cooling water of a first cooling circuit and a second chamber configured to store cooling water of a second cooling circuit by a partition wall; a first electric water pump integrally coupled to the first chamber of the integrated reservoir tank and configured to transmit the cooling water stored in the first chamber along a cooling water line of the first cooling circuit; and a second electric water pump integrally coupled to the second chamber of the integrated reservoir tank and configured to transmit the cooling water stored in the second chamber along a cooling water line of the second cooling circuit.