Abstract The preparation method and the sensing properties (sensitivity and selectivity to interfering gases) towards carbon monoxide of the new ternary compound Sn 1- x Fe x O y deposited in the form of thin films, are presented in this paper. The metal of the VIIIB group is introduced with concentrations in the range 0< x<25 at %. Thin films are sputtered using the RGTO (rhotaxial growth and thermal oxidation) technique. This technique consists of metal deposition onto a substrate maintained at a temperature higher than the metal melting point and metal oxidation by means of an annealing cycle in pure oxygen. Particular emphasis is given to the relations between some preparation parameters of the material, namely the atomic percentage ofiron or the annealing cycle, and to the sensor sensitivity towards CO and other interfering gases like C 2H 5OH, H 2 and NO x diluted in dry air. A sensitivity S= (G gas- G air )/ G air=3.5 towards 10 ppm of CO has been measured: the kinetic characteristics of the sensors are also presented, together with the working mechanism.