We investigated the oxidation of sputtered metallic Sn thin films annealed by N 2 atmospheric pressure plasma jets (APPJs) with and without the introduction of ambient air to the reaction. As the APPJ annealing duration increased, the metallic Sn first oxidized into SnO, and then, a metallic Sn phase reappeared owing to the disproportionation reaction 4SnO → Sn 3 O 4 + Sn → 2Sn + 2SnO 2 . The invol-vement of O 2 from the ambient air led to more reactive oxidation of the thin films. APPJ annealing increased the band gap to ∼2.6–2.7 eV. All the annealed films show conductivity with unstable read-ings of carrier types because of the mixed phases of Sn, SnO, and possibly, some SnO 2 in the films.