Mn2+-doped M2Si5N8 (M=Ca, Sr, Ba) phosphors have been prepared by a solid-state reaction method at high temperature and their photoluminescence properties were investigated. The Mn2+-activated M2Si5N8 phosphors exhibit narrow emission bands in the wavelength range of 500–700 nm with peak center at about 599, 606 and 567 nm for M=Ca, Sr, Ba, respectively, due to the 4T1(4G)¿6A1(6S) transition of Mn2+. The long-wavelength emission of Mn2+ ion in the host of M2Si5N8 is attributed to the effect of a strong crystal-field of Mn2+ in the nitrogen coordination environment. Also it is observed that there exists energy transfer between M2Si5N8 host lattice and activator (Mn2+). The potential applications of these phosphors have been pointed out.