magnetoelastic surface waves have been propagated in an epitaxial gd-ga doped yig film using piezoelectric zno layer and interdigital transducers for launching rayleigh waves at 339. 9mhz an in-plane applied magnetic field has been adjusted to obtain the magnetoelastic (me) interaction; in this case the waves become leaky. such an interaction has been investigated by optical diffraction in the raman-nath region with a polarized laser beam (6 328 a). a diffracted light, cross-polarized with respect to the input, has been detected when the me interaction exists. this signal due to the magnetic part of the wave can be used to study the characteristics of the interaction. the saturation threshold in acoustic power has been measured. then the behavior of the me interaction as a function of the magnetic field has been observed at different distances along the propagation path. the imaginary part (im. k) of the wave number k due to the leaky character of the interaction has been measured. moreover it is seen that the dynamic magnetization components can be analysed by faraday and cotton-mouton effects