Er3+ doped GSAG laser crystal with high optical quality was grown successfully by the Czochralski method for the first time. The structural parameters and the high crystalline quality of this crystal were determined. Juddofelt (J-O) parameterization scheme was applied to analyze the absorption spectra at room temperature. Accordingly, the lines strengths, oscillator strengths, transition probabilities, fluorescence branching ratios, and radiative lifetimes were calculated to characterize the laser properties of Er: GSAG crystal. Additionally, the fluorescence spectra and lifetimes of Er: GSAG crystal were measured and studied. The stimulated emission cross-section spectra and gain cross-section spectra were evaluated for I-4(13/2) -> I-4(15/2) (1.5-1.6 mu m) transitions which indicate high potential of 1 at% Er: GSAG for laser emissions at 1567 and 1605 nm. Furthermore, the possibility of Er: GSAG crystal to realize the visible laser output pumped by the GaN LDs were initially studied and analyzed.