In the current work the activity of Pt/Al2O3 and Pt/TiO2 catalysts in the reaction of NH3 oxidation was studied depending on the calcination temperature. A combination of XRD, TEM, XPS and TPR methods was applied in order to analyze the influence of the interaction between active component and support on the catalytic properties of the samples. Catalysts were prepared by incipient wetness impregnation using the Pt(NO3)4 solution with calcination at 400, 600 and 800°C. A highly dispersed Pt0 particles with the average particles size ∼1nm were observed after calcination at 400°C for both Pt/Al2O3 and Pt/TiO2 samples. However, Pt/TiO2 catalyst showed better catalytic characteristics at the low-temperature range with the temperature of 50% NH3 conversion (T50) about 175°C. The calcination of the Pt/Al2O3 catalyst at T>400°C improved the low-temperature activity due to the formation of large Pt0 particles. The T50 value did not vary significantly for Pt/TiO2 samples calcined at different temperatures. Based on XPS, XRD and TPR-H2 data the strong metal-support interaction (SMSI) was shown for Pt/TiO2 catalysts. SMSI resulted in the stabilization of platinum in a highly dispersed state even after high temperature calcination. Pt/Al2O3 sample calcined at 800°C had the highest specific catalytic rate of NH3 oxidation. The high activity of the catalyst is likely due to the presence of Pt0 particles with optimal size distribution.