The resonance spectrum of Gd3+ in LaAlO3 was investigated as a function of the temperature. It was found that the trigonal parameter b20 changes smoothly from 67×10-4 cm-1 at 689°K to 491×10-4 cm-1 at 20°K. The transition to cubic phase is found by extrapolation to be at 720+/-15°K. The spin Hamiltonian appropriate to the trigonal phase is given by H=gβH.S+B20O20+B40O40+B60O60+B43O43+B63O63+B66O66. The evaluation of the magnitude of the various parameters Bmn is presented.