The In₂O₃ thin films were fabricated on a alumina substrate by spin-coating method and the gas sensing properties were tested. The coating solution was synthesized by the mixing of aqueous solution of In(OH)₃ and acetic acid, and ammonium carboxymethyl cellulose as a binder. The In₂O₃ thin films between 71 and 210nm thick were obtained by spin-coating between 1 and 7 times followed by drying at 110 ℃ and calcining at 600 ℃. The films consisted of a dense stack of tiny In₂O₃ particles between 23 and 27nm in diameter and covered well large grains of the alumina substrate. Then film thickness was well controlled by the number of spin-coating. The fabricated In₂O₃ films showed high sensitivity and very fast response property to CO and Hz.