We investigated the upconversion (UC) emissions and their ambient dependences of SrTiO3 polycrystals co-doped in Er3+ and Yb3+ at different substitution sites. i.e., the A-site and B-sites in ABO(3)-type perovskite, and its response to H-2 and O-2 ambient annealing. Under near-infrared excitation at 980 nm, the as-synthesized samples exhibited strong UC emission features in the green (525 and 550 nm) and red (660 nm) region from Er3+ ions owing to sensitization by Yb3+; the emission was much stronger for A-site doping than for B-site doping. Interestingly, annealing in the H-2 atmosphere to increase the oxygen vacancies suppressed the photoluminescence and UC emission of the A-site doped samples, but enhanced the emission signals of the B-site doped samples. After subsequent annealing in the O-2 atmosphere to decrease the oxygen vacancies, the emission intensities showed a tendency to return to those in the as-synthesized A-site doped and B-site doped samples. These intriguing behaviors were explained in terms of the relationship between the substitution site and charge compensation. We performed the temperature dependent UC emissions and found that the intensity ratio between two green emissions changed significantly with temperature. This strong fluorescence intensity ratio could be used for optical thermometry.