Sr$_{l-x}$Ba$_{x}$Al$_2$O$_4$:Eu (x = 0, 0.1, 0.2, and 0.3 mol) phosphor was synthesized by the hydrothermal method and its properties of photoluminescence and long-afterglow were investigated. The mixtures of Sr(NO$_3$)$_2$, Al(NO$_3$)$_3$9$H_2O$, and Eu(NO$_3$)$_3$$.$6$H_2O$ salts dissolved in distilled water, after controlling their pH by NH$_4$OH solution, put into an Autoclave reactor with high temperature and pressure to react. Such synthesized SrAl$_2$O$_4$:Eu powders showed homogeneous and ultra-fine particles of sub-micron size. In order to have the photoluminescence characteristic, powders were heat treated at 1100 -140$0^{circ}C$ for 2 h in Ar/H$_2$ reduction atmosphere. Photoluminescence spectra showed a excitation along the wide wavelength of 250 ∼ 450 nm, and broaden emission with maxima peak at 520 nm. Also, it showed a good long afterglow with decaying over 1000 sec after excitation illumination for 10 min. In addition, the microstructure and crystal structure of SrAl$_2$O$_4$:Eu powders were investigated by an SEM and XRD, respectively.ely.