Eu2+ and Eu2+–Mn2+ codoped (Ba,Sr)Mg2Al6Si9O30 phosphors have been synthesized by solid state reaction, and their luminescent properties are investigated. Under the excitation of 330 nm, it is observed that the emission of Eu2+ consists of two emission bands, located at around 370 and 450 nm, which are attributed to two Eu2+ centers (Eu2+(I) and Eu2+(II)) ions substituting for two different Ba2+ and Mg2+ sites, respectively. As Sr2+ gradually substitutes Ba2+, the emission bands of Eu2+(I) shift to longer wavelength whereas the emission bands of Eu2+(II) exhibit no change. This phenomenon is discussed in terms of the crystal-field strength. A detail analysis on the energy transfer from Eu2+ to Mn2+ in SrMg2Al6Si9O30 host is presented, which indicates the energy of the red emission of Mn2+ is derived mainly from Eu2+(I). We have also demonstrated that BaMg2Al6Si9O30:Eu2+, Mn2+ exhibits better thermal quenching properties than that of SrMg2Al6Si9O30:Eu2+, Mn2+ because of bigger activation energy.