The improvement in microwave dielectric characteristics by Ca substitution in SrLaAlO4 ceramics together with the stability of K2NiF4 structure were investigated. X-ray diffraction analysis and the scattering electron images combined with EDS analysis indicated that the matrix phase was a solid solution with a composition represented by the chemical formula Sr1−xCaxLaAlO4 in the entire range of 0≤x≤0.9, and minor amount of LaAlO3 secondary phase was detected only in the composition of x=0.8 and 0.9. The relative permittivity increased slightly with increasing x, while the temperature coefficient of resonant frequency was tuned from −33.9 to −14.7 ppm/°C. The significant improvement of Qf value was achieved in the present ceramics with increasing x and reached the maximum at x=0.4, but it turned to decrease for x>0.4. The best combination of microwave dielectric characteristics was achieved at x=0.4: ɛr=18.1, Qf=150 500 GHz, and τf=−26.2 ppm/°C.