Perovskite-related Ga oxide, Sr₃(Ga_1-xMn_x)₂O₆ (0≤x≤0.2) was synthesized and characterized in order to design new diluted magnetic perovskites for spin electronics. The crystal structure of Sr₃(Ga_1-xMn_x)₂O₆ (SGMO) was investigated by powder X-ray diffraction and Rietveld analysis. Knowledge of the SGMO was refined using the Rietveld program, RIETAN. Strontium gallate Sr₃Ga₂O₆ (SGO) is a novel cubic structure with GaO₄ tetrahedral unit, space group P3a, and a=b=c=16.095 Å. The crystal structure of SGMO is similar to that of SGO, and Mn-doping does not affect the crystal structure of the mother compound SGO. The electronic nature of Ga and Mn ions in SGMO was investigated by X-ray photoemission spectroscopic measurement, suggesting that the ions of Ga and Mn are +3 and +4 states, respectively. Magnetic properties of SGMO were measured on a SQUID magnetometer. SGMO exhibits non-paramagnetic behavior at 10 K, but it is paramagnetic with θ_P<0 at 300 K.