Oxygen substitution was carried out on Li₁₀SiP₂S₁₂ (LSiPS) which has the Li₁₀GeP₂S₁₂ (LGPS) type crystalline structure. The general formula of Li₁₀SiP₂S_12-xO_x (LSiPSO) where 0 ≤ x ≤ 1.75 was set for solid state reaction to produce oxy-sulfide sites. The phase distribution and local structural units of LSiPSO were determined by powder X-ray diffraction (PXRD), and Raman, FT-IR,²⁹Si and ³¹P Solid State NMR spectroscopies. The LGPS like LSiPSO phase increased while the impurity phase, β-Li₃PS₄ was reduced and formed Li₃PO₄ phase by O substitution. The optimized lithium ionic conductivity was found for x = 0.7 at 3.1 x 10^-3 S/cm at 25℃. However, for the higher doped oxygen such as x > 0.9, a degradation of LSiPSO occurs and it is also expected to become the Li₃PO₄ phase which leads to a decrease in the ionic conductivity. The local structural units was determined by ³¹P and ²⁹Si NMR and spectrum deconvolution to show sulfide, oxide and mixed oxy-sulfide local units. On the other hand, the doped O was found that only incorporating with phosphate centered tetrahedral unit such as PS_4-xO_x during no pure orthosilicate SiO₄^4- units were observed, even at the highest x examined.