Abstract: Astudy has been made of binary salts'system KNO₃-KCl by the methods of DTA, visual polythermal and X-ray powder diffraction. An incongruently melting compound KNO₃·KCl which decomposes at 359℃ andtransittes at 124℃ and 271℃ has been found in the system. Peritectic point of this compound lies in the composition containing 12.5wt% KCl. The values of the eutectic between KNO₃ and KNO₃·KCl are 318℃ and 5.0wt% KCl. Another metastable compound 4KNO₃ KCl incongruently melting at 342℃ may also existes in this system. From the results of DTAand X-ray diffraction, no evidence was found for solid solution on the both sides of KNO₃ and KCl.