A novel Fe2O3–CaSiO3 (FCS) composite microwave dielectric ceramic was prepared by a solid-state reaction method (SSR). The phase composition, microstructure and relative density of the composite ceramics were systematically investigated and their relationship with microwave dielectric properties was investigated. The phase compositions of the prepared samples were CaSiO3 and Fe2O3 in all sintering temperatures. The phase fractions and cell parameters of the FCS ceramics were analyzed by Rietveld refinement. Besides, the Q × f values of the FCS ceramics were positively correlated with the phase content of CaSiO3. The effect of microscopic morphology on the microwave dielectric properties of the FCS ceramic samples was investigated by SEM technique. EDS analysis verified that the phase composition of the ceramic samples was Fe2O3 and CaSiO3. Finally, the FCS ceramics sintered at 1180 °C for 4 h obtained excellent microwave dielectric properties of εr = 8.69, Q × f = 28,000 GHz, τf = − 24.29 ppm/°C.