This work aims at demonstrating a relationship between the propane oxidation reaction mechanism and the chemical/physical properties of the Mo-V-Sb-Nb mixed oxide catalyst, calcined (500/600degreesC) and activated (500degreesC) under oxidative and inert conditions. Calcination and activation under inert conditions yields a catalyst with complex mixed oxides phases (Sb4Mo10O31, (My5+Moz5+Mo1-y-z6+)(5)O-14, etc.) and a partial reduced total oxidation state, which favours the formation of propene as the sole primary product and acrylic acid as a major secondary product. In contrast, catalysts calcined and/or activated in an oxidative atmosphere give more oxidised phases (MoO3 as a major phase), which results in the preferable formation of acetic acid via a route which bypasses propene as an intermediate.