We have investigated the effect of high-temperature post-annealing and control of excess oxygen for La1-xSrxMnOy (0.05 ≤ × ≤ 0.2) single crystals. Thin plate-like single crystals prepared by careful cutting and polishing enabled the control of excess oxygen for the single crystals by post-annealing for relatively short times at various temperatures. Post-annealed crystals with y ∼ 3.00 exhibited higher T C than as-grown crystals due to a homogenization of cation and oxygen compositions and reduction of local lattice strains. With an increase of y, TC systematically increased for all Sr compositions. Competition between an increase of mean valence of manganese and a generation of cation vacancies determines the TC of La1-xSrxMnO y crystals.