Effects of pores on the microwave properties in microwave dielectric ceramics were studied by a computer simulation. Scattering matrix S$\_$21/ obtained from the network analyzer was compared to the S$\_$21/ obtained from the simulation. From electric field distribution, the dominant resonant TE$\_$01$delta$/ mode could be easily determined. The effects of the porosity and pore size inside the dielectrics on the microwave properties were investigated by the HFSS simulation. When the total pore volume remains constantly, the quality factor decreased as the pore size Increases. As the total pore volume of the dielectrics increased. quality factor decreased.