Bismuth-free yttrium iron garnet and Bismuth-doped iron garnet magnetic thin films have grown on gadolinium gallium garnet single crystal substrates by means of the liquid phase epitaxy method. Faraday rotation measurement results show clearly a strong enhancement with bismuth doped sample. The second harmonic generation measurements in transmission show a relation with the orientation of the spontaneous magnetization vector of films and the second harmonic intensities.