The stabilization of La2/3TiO3 in the perovskite structure by 4 mol% LaAlO3 resulted in maximum values for the relative permittivity (k＇approximate to 72) and temperature coefficient of resonant frequency (tau(f) = 123 ppmK(-1)). The Q-value (quality factor) of these ceramics were over 5300 measured at 4.5 GHz. Higher contents of LaAlO3 cause a decrease in both the permittivity and tau(f) values, accompanied by an increase in the Q-value. Typical values measured at 6.0 GHz for ceramics with the composition 70 mol% La2/3TiO3-30 mol% LaAlO3 are k＇ > 44, tau(f) = +7 ppmK(-1) and Q > 5500. The results depend on the processing parameters. The sintering temperature increases with increasing LaAlO3 content. An oxidizing sintering atmosphere improves the Q-value, whereas the permittivity and tau(f) are not significantly affected.