Abstract Micro-CaCu3Ti3.95Zr0.05O12 (CCTZO) ceramics were prepared by a sol–gel method and sintered at 1050°C for different times. The particle sizes and dielectric permittivity simultaneously increase with the sintering time. The permittivity of CCTZO sintered for 24h is 3.3×105 at 100Hz, markedly higher than that of CCTZO sintered for 1h and 12h. On the contrary, the permittivity of CCTZO/PI films declines with the sintering time. The permittivity of CCTZO (sintered for 1h)/PI film with 40vol% filler is 64 at 100Hz, higher than those of the CCTZO (sintered for 24h and 12h)/PI film. This indicates that the permittivity of CCTZO/PI composites was affected more by the particle size than the permittivity of CCTZO ceramics, and we can draw a conclusion that the dielectric mechanism of micro-ceramic/polymer composites comes mainly from interfacial polarization effect.