K4Fe(CN)6·3H2O was studied by a derivatograph in the temperature range +20° to +300° and dielectric constant (ε) measured from −80° to +150°. The loss of the three water molecules occurs at 105° and theε vs T curve shows a Debye relaxation behavior. By using Mason's theory it was possible to classify K4Fe(CN)6·3H2O in the temperature range −25° to +100° C as a para-electric order-disorder crystal.