The temperature variation of the far-infrared AFMR frequency in the quadratic layer antiferromagnets K 2 NiF 4 and Rb 2 NiF 4 has been measured using Fourier transform interferometry techniques. The results are found to be sharply defferent from those in usual three-dimensional antiferro-magnets. Oguchi-Honma's spin wave theory applied to the two-demensional systems is shown to predict properly the observed behaviours.