La 2/3 Ca 1/3 MnO 3 and Se 2 FeMoO 6 nano-crystalline powders were pre-prepared using the polymer-network gel method, and the average grain sizes of La 2/3 Ca 1/3 MnO 3 and Se 2 FeMoO 6 were about 40 and 50nm, respectively. A series of La 2/3 Ca 1/3 MnO 3 /Se 2 FeMoO 6 nano-crystalline composites (molar ratio 1:1) were successfully synthesized under high pressure (4GPa) and different treating temperatures. Due to the compositive influence of the smaller grain sizes, the Curie transition temperatures T C (∼225K) for all composites are lower than that of the pure phase La 2/3 Ca 1/3 MnO 3 . For the sample synthesized at the optimum conditions, the magnetoresistance value is close to 32% at 3T and 5K.