La3Ga5SiO14 (LGS) thin films have been grown by r.f. sputtering at 600 degrees C on (200)-textured MgO buffer layers deposited also by r.f. sputtering on Si substrates. The evolution of crystalline phases in the thin films as a function of time was examined by X-ray diffraction and scanning electron microscopy before and after annealing in air for various times. The morphology of the crystals formed and their formation mechanism were discussed.