Angular selectivity of holographic gratings (i.e, the width and the shape of the grating diffraction efficiency angular dependence curve) recorded in a-As2S3 and a-As40S15Se45 of different thickness and with different periods has been experimentally studied with 632.8 nm He-Ne laser readout light depending on the diffraction order number modulus, m = 1,2,3. It is found that angular selectivity increases when the modulus of the diffraction order number is increased. Besides, the asymmetry of the angular selectivity also increases when the diffraction order number modulus is increased. The obtained results can be largely explained on the basis of thin and thick grating equations as well as using Kogelnik’s coupled wave theory. The angular selectivity increase in higher diffraction orders can be used for the production of more efficient holographic optical elements and for studies of films and photoinduced processes.