© 2016, Springer Science+Business Media Dordrecht. Abstract: Undoped In 2 O 3 and 0.25–1.00 wt% M (M=Pt, Nb, and Ru)-doped/loaded In 2 O 3 nanoparticles were successfully synthesized in a single-step flame spray pyrolysis technique using indium nitrate, platinum (II) acetylacetonate, niobium ethoxide, and ruthenium (III) acetylacetonate precursors. The undoped In 2 O 3 and M-doped In 2 O 3 nanoparticles were characterized by Brunauer–Emmett–Teller (BET) analysis, X-ray diffraction (XRD), and scanning and transmission electron microscopy (SEM & TEM). The BET average diameter of spherical nanoparticles was found to be in the range of 10.2–15.2 nm under 5/5 (precursor/oxygen) flame conditions. All XRD peaks were confirmed to correspond to the cubic structure of In 2 O 3 . TEM images showed that there is no Pt nanoparticle loaded on In 2 O 3 surface, suggesting that Pt should form solid solution with the In 2 O 3 lattice. Gas sensing studies showed that 0.5 wt% Pt doping in In 2 O 3 nanoparticles gave a significant enhancement of NO 2 sensing performances in terms of sensor response and selectivity. 0.5 wt% Pt/In 2 O 3 exhibited a high NO 2 response of ~1904 to 5 ppm NO 2 at 250 °C and good NO 2 selectivity against NO, H 2 S, H 2 , and C 2 H 5 OH. In contrast, Nb and Ru loading resulted in deteriorated NO 2 response. Therefore, Pt is demonstrated to be an effective additive to enhance NO 2 sensing performances of In 2 O 3 -based sensors. Graphical Abstract: [Figure not available: see fulltext.]