Öz The structures of Mg- and Sr-doped $\beta $-Ca$_{2}$SiO$_{4}$ have been established from high-resolution synchrotron X-ray powder diffraction. These silicates are all isostructural and the structures have been refined in the monoclinic space group, $P$2$_{1}$/$n$. As expected based on size arguments, the cell parameters increase as the amount of Sr increases and likewise decrease as the amount of Mg increases due the size effects of the dopant cation. In all cases the SiO$_{4}$ tetrahedra are essentially regular.