The magnetic (x,T) phase diagram of the solid solution NdRh 2−x Ru x Si 2 (ThCr 2 Si 2 -type of crystal structure) has been established based on the neutron diffraction data and supplemented by magnetometric data. A collinear antiferromagnetic order AFI described by the wave vector k=(0,0,1) changes with an increase of Ru concentration to a sine modulated with the wave vector k=(0,0,k z ). For x=1.6 ferromagnetic order is observed. In the region 1.7⩽x⩽2.0 the ferromagnetic order at low temperatures changes with increasing temperature to a sine modulated structure described by the wave vector k=(k x ,k x ,0).