Microwave dielectric properties of solid solutions in the system ZrTiO4-HfTiO4 were measured for quenched and slow-cooled specimens. The relative permittivity of the quenched specimen decreased with increasing Hf content; that of the slowly cooled specimen had a peak permittivity value for the composition containing 75 mol% of ZrTiO4. These results are almost identical with those reported at 1 kHz. A specimen with a zero temperature coefficient of resonant frequency was obtainable by optimizing the composition and heat treatment.