In this study, we demonstrate the temperature dependence of the dielectric properties of Al 2 O 3 and Ba 2 Ti 9 O 20 ceramics, using a probe-backside reflection (PBR) method, at frequencies range up to 320 GHz. The impact of transmission loss on the dielectric properties was first eliminated from the measured S-parameter values using the original S-parameter values of a transmission line. Although the temperature coefficient of dielectric permittivity was uncertain owing to limitations in the measurement repeatability of the PBR method, those of loss tangents of Al 2 O 3 and Ba 2 Ti 9 O 20 ceramics were calculated as 2.8 × 10 −5 K −1 and 1.1 × 10 −4 K −1 , respectively, for frequencies up to 125 GHz. Furthermore, the temperature coefficient of the dielectric permittivity of Al 2 O 3 was calculated as 691 ppm K −1 at 255 GHz, while those of the dielectric loss tangent at 235 GHz and 275 GHz was calculated as 1.2 × 10 −5 K −1 and 1.5 × 10 −5 K −1 , respectively.