The deactivation of a Pt/gamma-Al2O3 catalyst used in an industrial plant for the partial oxidation of methane to synthesis gas was investigated. Four samples at different time-on-stream in air were characterized and their catalytic performances were tested in a micro-reactor in order to shed light on the causes and the effects of this deactivation. The high temperatures (about 900degreesC) reached while operating in the industrial plant, promoted modifications to the gamma-Al2O3, inducing sintering phenomena and. therefore, deactivation effects. The not used sample showed good values of yield in syngas (compared with equilibrium values). but these performances decreased quickly with time-on-stream. (C) 2003 Elsevier Science B.V. All rights reserved.