An efficient green phosphor, Ba2MgSi2O7:Eu2+, was prepared by a solid-state reaction. Excited by 350-420 nm light, the phosphor shows a strong and broad emission band centering at 505 nm. The concentration quenching mechanism was verified to be a dipole-dipole interaction and the critical energy-transfer distance was confirmed as around 20 A by both the calculated crystal structure method and the experimental spectral method. This phosphor shows a low thermal-quenching property with an activation energy of 0.677 eV. Light-emitting diodes (LEDs) were fabricated with Ba2MgSi2O7:0.07Eu2+ and 395-nm-emitting InGaN chips and exhibited strong wide-band green emission and relatively stable current-dependent electroluminescence properties, indicating that this phosphor is a promising candidate as a green component for the fabrication of white LEDs.