Compositions in the (1-x)LaAlO3-xSrTiO(3) system were prepared in order to compensate the negative temperature coefficient of the resonant frequency (tau(f)) of LaAlO3. Their microwave dielectric properties and crystal structure were investigated. Powder X-ray diffraction patterns showed that LaAlO3 and SrTiO3 form a complete solid solution, but the permittivity and tau(f) values exhibited nonmonotonic mixture-like behavior. This peculiar behavior is discussed in terms of the structural trends in the system. The low permittivity and negative tau(f), of LaAlO3 appear to dominate the dielectric properties of the (I-x)LaAlO3-xSrTiO(3) system for SrTiO3 concentrations as high as 60%.