The reaction products from CeO2 and WOs were studied by quenching method and TG-DTA in air, oxygen and argon(Pe, =10 g atm) atmospheres at 650. v1400eC. Two new binary oxides, 2Ce20segWOs and Ce2Q3e2WOs, were found in addition to well--known Ce20se3 WO3. Their X-ray powder fraction pattems, chemical and mag etic properties, a d melting points and transition points were studied. The mp were 1026 10oC for 2Ce203.9 WO8, 1070 10. C for Ce203.3WO8, and 1395 10. C for Ce203, 2WO8. Ce203, 3WO8 and Ce303.2WO3 had the reversible tra sition point at 1005 10. C and 1105 10. C, respectively, Different products were obtained accerding to atmospheres and temperatures, even if same reactants were used, That is, Ce20s e 2 WOs was not stable and decomposed to Ce20se3WOs and CeO2 in air and oxygen, or in argon below 7900C, and Ce203.3WO3 was also unstable and decomposed to 2 Ce20s e g WO3 and CeO2 in air below 830 C, or in oxygen below 8900C. These results show that the preparation and decompositison of these compounds can be represented by the following equilibrium reactions, 4CeO2 9WOs=2Ce20s.9WOs +O2 (1)4CeOa +2(2 Ce20s.9 WOs)=6(Ce20s.3 WOs) + 02 (2)4CeO2 + 4(Ce20s e 3 WO3)=6(Ce20s, 2 WOs) + 02 (3)The phase relation for these equations in the equilibrium oxgen pressures was determined. The stable region o f each compound was shown in Po2-T diagram.