This paper describes Q factors of dielectric resonators for quasi-microwave filters. Dielectric resonators are composed of dielectric ceramics with different ε_r or tanδ and cylindrical cavities with different dimensions. Measured resonant frequencies and Q factors of dielectric resonators are compared with computed value by FEM and incremental frequency rule. As a result, low-loss dielectric ceramics are effective when Qd(the dielectric Q factor) is dominant for Q factor of dielectric resonator. In this case, the dielectric resonator with Qu=65000 is realized by using Ba(Zn_1/3Ta_2/3)O₃-(Sr, Ba)(Ga_1/2Ta_1/2)O₃. On the other hands, reducing conductor losses with using high εr dielectric ceramics are effective when Qc(the Q factor of conductor) is dominant for the Q factor of whole dielectric resonator.