Acoustooptic tunable filter (AOTF) is one of the most important devices in the high densed WDM system. One significant limitation of AOTF′s performance is the presence of sidelobes in the transmission spectra. It is proposed that the apodization can be accomplished by use of the electrooptical effect of LiNbO 3 crystal based on the principle of the birefringence apodization. This method is analyzed and discussed theoretically. The experimental results are consistent with the theoretical results on the whole.