Microwave dielectric ceramics NdNbO4 were prepared by conventional mixed oxide route. The effects of CaF2 addition on the microstructures and microwave dielectric properties of NdNbO4 ceramics were investigated systematically. Formation of second phase NdNb3O9 and CaNb2O6 can be detected at 0–1.0 wt.% CaF2 additions and 2.0 wt.% CaF2 additions, respectively. Variation of grain shapes were observed with CaF2 content increasing. The microwave dielectric properties were affected by the amount of CaF2 addition. At 1225 °C for 4 h, NdNbO4 ceramics with 2.0 wt.% CaF2 possesses excellent microwave dielectric properties: εr = 20.1, a Q × ƒ = 75000 GHz and τƒ = −19.16 ppm/°C. There was more than two times increase in quality factor with 2.0 wt.% CaF2 doping in NdNbO4 ceramics.