This paper discussed the effect of composition on the afterglow phosphorescence of Sr4Al14O25: Eu2+, Dy3+ phosphors. The different composition did not make any difference on the emission peaks of the phosphors. All the phosphors show a broad band emission peak at λ=490 nm. However, long afterglow properties of the phosphors were influenced by the composition of starting materials. Al-rich phosphors have better long afterglow properties with high emission intensity and longer decay time than the phosphors rich in Sr, which can be ascribed to the different trap levels and trap concentrations formed in the hosts.