The thermally conductive（TC）polymer composites filled with thermally conductive inorganic fillers were prepared with melt mixing.The influence of such essential factors as size and filler material on the thermal conductivity and electrical resistivity of the composites was investigated.The results showed that with the reduction of filler size，the thermal conductivity of the composites decreased，however the electrical conductivity increased，and that with increasing volume fraction of filler，the thermal conductivity of composites rose gradually.The changes in the thermal conductivity of composites were not as rapid as those of the electrical conductivity of composites.A mechanism was suggested to explain the difference mentioned above between the thermal conductivity and the electrical conductivity of the compositesHeat conduction of the composites may be due to thermal vibration transmission.