Oxide phosphorescent phosphor has an wide application in ceramic art and decoration due to its chemical and mechanical properties. Here, phosphorescent properties of strontium aluminate phosphor ($SrAl_2O_4:Eu^{2+}$, $Dy^{3+}$) emitting yellowish-green light was investigated with thermal treatment at $1250^{circ}C$ under air and reducing atmosphere. The characterizations of thermally treated samples were analyzed using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), fluorescence spectrometer. $SrAl_2O_4:Eu^{2+}$, $Dy^{3+}$ still showed a good phosphorescent properties after annealing process in reducing atmosphere, while phosphorescence of $SrAl_2O_4:Eu^{2+}$, $Dy^{3+}$ annealed in air seriously degraded, due to oxidation of $Eu^{2+}$ to $Eu^{3+}$ ions. It was also observed that $SrAl_2O_4:Eu^{2+}$, $Dy^{3+}$ annealed in reducing atmosphere emitted yellowish-green light during 3 h after being exposed to sunlight.