To provide a practical matrix for iontophoresis with markedly improved drug availability. A system for iontophoreses, which comprises an anode side matrix and a cathode side matrix, wherein the anode side matrix contains a cationized drug and the cathode side matrix contains a water soluble acidic substance. A matrix for iontophoreses comprising a drug reservoir containing a drug, the drug reservoir having a thickness of less than 0.05 mm. Iontophoresis using the iontophoretic matrix of the present invention makes it possible to administer a drug to the body at high availability.