The (La1-xSmx)NbO4 (x=0-0.10) ceramics were prepared by the conventional solid-state reaction method. The microstructure and the microwave dielectric properties were discussed in detail. The X-ray diffraction patterns of (La1-xSmx)NbO4 (x=0-0.10) showed that only a single monoclinic fergusonite structure of LaNbO4 could be found. The dielectric constant (epsilon(r)) was affected by the dielectric polarizabilities and the B-site bond valence. The variation trend of Qxf(0) was in accordance with packing fraction. The temperature coefficient of resonant frequency ((f)) had a close relationship with the B-site bond valence, which was determined by the bond strength and bond length. When sintered at 1325 degrees C for 4hours, the (La1-xSmx)NbO4 ceramics with x=0.08 exhibited enhanced microwave dielectric properties: epsilon(r)=19.37, Qxf(0)=62203GHz and (f)=2.57ppm/degrees C. In addition, we made an overview about the ceramics that possess the same packing fraction and bond valence relationships, the results show that this structure-property relationship has a wide applicability.