Novel LaMgAl11O19:Tm3+, Dy3+ phosphors were prepared utilizing a high-temperature solid-state reaction method. The phase formation, luminescence properties, energy-transfer mechanism from the Tm3+ to the Dy3+ ions, the thermal stability, and CIE coordinates were investigated. When excited at 359nm, the LaMgAl11O19: xTm(3+) phosphors exhibit strong blue emission bands at 455nm. After codoping with Dy3+ and excitation at 359nm, the LaMgAl11O19:0.03Tm(3+), yDy(3+) phosphors emitted white light consisting of the characteristic emission peaks of Tm3+ and Dy3+. The Dy3+ emission intensity increased with the Dy3+ concentration due to the energy transfer from Tm3+ to Dy3+, and concentration quenching due to the high Dy3+ doping concentration (y=0.1mol) did not occur. The calculation of the CIE coordinates of the LaMgAl11O19:Tm3+, yDy(3+) phosphors revealed the tunability of the emission color from blue to bluish-white and to white by changing the excitation wavelength and the doping concentration. An energy transfer from Tm3+ to Dy3+ by dipole-dipole interaction was confirmed by the decay curve, lifetime, and energy-transfer efficiency measurements. When excited at 359nm, the LaMgAl11O19:Tm3+, Dy3+ phosphor also showed good thermal stability, suggesting that it can be used in white LEDs excited by a GaN-based ultraviolet LED.