Pb((Mg1/3Nb2/3)0.7(Zn1/3Nb2/3)0.3)O3 (PMZN) relaxor ferroelectric ceramics produced by a reaction-sintering process were investigated. Without any calcination, the mixture of PbO, Mg(NO3)2, Zn(NO3)2 and Nb2O5 was pressed into pellets and sintered directly. PMZN ceramics of 100% perovskite phase were obtained. Density of 8.11 g/cm3 (> 98% of theoretical value) was obtained after sintered at 1200°C for 2 h. 3–9 μm grain size was obtained in PMZN ceramics sintered at 1180°C–1250°C for two hours by reaction-sintering process. Dielectric constant at room temperature under 1 kHz reaches 18200 after sintered at 1200°C for 2 h.