The long afterglow phosphor SrAl2O4:Eu2+, Dy3+ with various particle size and shape were prepared by solid state reaction at 1200~1500°C for 3 h. In the synthesis, five kinds of α-Al2O3 were used as the starting materials, whose particle size ranged between submicron and a hundred micron orders. The peak intensity of excitation and emission spectra and the afterglow life time depended on the size of calcined particle, showing the higher performance with the larger particle size. SrAl2O4:Eu2+, Dy3+ synthesized using the alumina with a few micron size of primary particle but forming 50 μm of secondary particles showed high particle growth rate even at the low calcination temperature of 1200°C, giving almost the similar particle size until at 1500°C. Accordingly, the phosphorescence property was also independent on the calcined temperature. On the other hand, SrAl2O4:Eu2+, Dy3+ prepared from the alumina with 0.1~0.5 μm of dispersed particles depended largely on the calcined temperature, showing the highest performance for the samples prepared at 1400~1500°C. The large particles with smooth surface were effective for the high emission and afterglow properties.