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/degrees 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: epsilon(r)=18.1, Qf=150 500 GHz, and tau(f)=-26.2 ppm/degrees C.