A possibility to produce microwave (MW) dielectric materials by liquid-phase sintering of fine particles was investigated. Zn3Nb2O8 powders with a grain size 50-300 nm were obtained by the thermal decomposition of freeze-dried Zn-Nb hydroxides or frozen oxalate solutions. The crystallization of Zn3Nb2O8 from amorphous decomposition products was often accompanied by the simultaneous formation of ZnNb2O6. Maximum sintering activity was observed for single-phase crystalline Zn3Nb2O8 powders obtained at the lowest temperature. The sintering of as-obtained powders with CuO-V2O5 sintering aids results in producing MW dielectric ceramics with a density 93%-97% of the theoretical, and a Q x f product up to 36 000 GHz at sintering temperature (T-s)>= 680 degrees C. The high level of MW dielectric properties of ceramics was ensured by intensive grain growth during the densification and the thermal processing of ceramics.