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Sn‐Ti submicrospheres with tunable particle size were successfully synthesized by adjusting the water amount over Polyvinylpyrrolidone(PVP)‐assisted sol‐gel method in this paper, and the effect of the submicrosphere size on the catalytic performance in the B‐V oxidation of cyclohexanone by molecular oxygen was also investigated. Their physical and chemical properties were character‐ rized by Scanning electron microscope (SEM), X‐ray diffraction (XRD), N2 sorption, Pyridine‐adsorbed IR(Py‐IR), Uvioletvisible diffuse reflection spectroscopy(UV‐vis), X‐ray photoelectron spectra (XPS), Transmission electron microscope and Energy dispersive X‐ray detector(TEM‐EDX) techniques. The characterization results showed that the Sn‐Ti crystal phase would be affected by the initial water amount resulting in the variation for the incorporation of tin species into the tetrahedral TiO2. The regular Sn‐Ti submicrospheres with particle size about 210±5 nm and typical Lewis acidities for MTS‐W‐4.0 sample can be obtained when water amount was as high as 4.0 mL, and it exhibited higher catalytic performance than other catalysts where its ϵ‐caprolactone yield was 97.8 %. Compared to the decline range of 13.6 % with the submicrospheres particle size as about 450 nm, the drop of ϵ‐caprolactone yield was only 3.9 % and the yield of ϵ‐caprolactone can be kept at 93.9 % over MTS‐W‐4.0 sample after repeated use for 5 times. [ABSTRACT FROM AUTHOR]