The apparatus of Faraday effect LMR used for the detection of 14N 16O and 15N 16O is described in this paper. We gave and analyzed the spectra of FLMR of 14N 16OX2pi3/2 (1. 5) v =0-->1 transition and 15N 16OX2pi3/2Q(1.5) v =0-->1 transition. The dependence of FLMR signal on the sample molecular concentration has been stadied.