Abstract: A multi-layer dielectric resonant device has a dielectric resonator and a microstrip line to be coupled to the dielectric resonator. The dielectric resonator includes a first dielectric layer, a second dielectric layer, a third dielectric layer, a metallic substrate and a metallic plate. The second dielectric layer is placed on the first dielectric layer and has a dielectric constant higher than that of the first dielectric layer. The third dielectric layer is placed on the second dielectric layer and has a dielectric constant lower than that of the second dielectric layer. The metallic substrate is placed in the center portion of the second dielectric constant layer to reduce the conductor loss of the dielectric resonator. The metallic plate constitutes the outer wall of the dielectric resonator.