Metal doping into semiconductor metal oxides has been considered to be an effective method to improve photocatalytic activity owing to its advantage in tuning the electronic structure and alleviating charge carrier recombination. In the present work, we emphasize on the effect of Sr doping on the photacatalytic performance of SnO2 nanoparticles (NPs). XRD patterns and FESEM with EDX results suggest that Sr-doped SnO2 NPs have been crystallized in a single phase tetragonal rutile structure. Optical absorption study shows the band gap narrowing of SnO2 NPs with Sr content. Several techniques such as x-ray photoelectron spectroscopy (XPS), soft x-ray absorption spectroscopy (SXAS) at O K-edge and photoluminescence (PL) analysis reveal the presence of oxygen vacancies in Sr-doped SnO2 NPs which are responsible for improved photocatalytic performance. Due to high oxygen vacancy concentration in contrast to pure and 3% Sr-doped SnO2, Sr-doped SnO2 with 5% doping content exhibits the outstanding photocatalytic performance and can degrade 94% MB in 60 min and 82% Dinoseb in 120 min, respectively under UV light illumination. This remarkable improved photocatalytic activity could be credited to the fact that Sr2+ doping may facilitate the separation of charge carrier through trapping sites created by Sr ions as well as by the creation of oxygen vacancy.