The structure of the 4d Rydberg term complex of the nitric oxide molecule has been studied by rotational analyses of the following bands photographed with spectrographs of high resolving power: (i) the weak band 4d–X2Π observed at 1470 Å in the absorption spectrum, (ii) the group 4d–3p of Rydberg–Rydberg bands observed as 4d–C2Π (6400 Å) and 4d–D2Σ+ (6800 Å) bands in the emission spectrum of a discharge. A type of l uncoupling of the Rydberg electron of the molecule is found very similar to the case already known for the 3d complex of NO. Constants characterizing the d complexes are calculated, and a comparison of the 3d and 4d complex is made.