La (Mg0.5 Ti (0.5-x) Snx) O3 perovskite ceramics with composition (x=0.0-0.5) are prepared by the solid state reaction method. The ceramics are characterized by x-ray diffraction, far-infrared reflectance, Raman spectroscopy, and microwave dielectric properties. The symmetry of ceramics is monoclinic with P 21 /n space group. Intrinsic dielectric constant and loss are estimated by fitting reflectance to the four-parameter semiquantum model. Transverse optic phonon mode strengths and average phonon damping are calculated. The modes corresponding to B -site ordering are identified in Raman spectra and the A1g mode of La (MgTi) 0.5 O3 is analyzed by assuming two merging modes. The variation of long-range order is correlated with full width half maximum of the A1g mode. Microwave measurements are carried out in the frequency range of 8-10 GHz. The dielectric constant (ε′) is found to gradually decrease from 28.4 to 19.7 with an increase in tin concentration, whereas the temperature coefficient of resonant frequency (τf) decreases from -68 to -84 ppm/°C. The product of the quality factor and resonant frequency (Q×f) obtained for La (MgTi) 0.5 O3 is 55,000 GHz, that decreases to 46,000 for x=0.25 composition and then increases to 63,000 GHz for La (MgSn) 0.5 O3. © 2007 American Institute of Physics.