(Sr, Ca)2SiO4:Eu2+ nanopowders were prepared by a co-precipitation method, and then the effects of Ca2+ ions on the structural and luminescent properties were investigated. The pure Sr2SiO4:Eu2+ powders were perfectly composed of the beta-phase, whereas the substitution of Ca2+ ions led to the beta --> alpha' phase transition. The photoluminescence spectra of Sr2SiO4:Eu2+ exhibited two excitation bands at around 330 and 375 nm assigned to Eu(I) and (II) sites, respectively, resulting in two emission bands at around 473 and 543 nm. Meanwhile, the dominant peak wavelengths of the emission spectra of (Sr, Ca)2SiO4:Eu2+ could be tuned, depending on the cation ratio of Ca2+ to Sr2+. The substitution of Ca2+ ions for Sr2+ ions caused the red-shift of the emission peaks of Sr(2-x)Ca(x)SiO4:Eu2+ powders with increasing Ca2+ content (x = 0-1.0) due to the increase in the crystal field strength.