V/P/O catalysts were prepared using isobutanol as solvent,which contained either cobalt or iron as the dopant (Me/V 0.01). The catalysts were characterized with several techniques, both after thermal treatment and after reaction in n-pentane/air. The catalytic performance was compared for the selective oxidation to maleic and phthalic anhydrides under conditions at which results were stable (i.e., after at least 200 h time-on-stream). It was found that iron had a dramatic effect on the structural evolution of the catalyst both during calcination and during aging; in contrast, the effect of cobalt was much less marked. Doping with 1% cobalt remarkably improved the selectivity to the phthalic anhydride at the expense of the maleic anhydride with respect to the undoped catalyst, while doping with iron led to a catalyst less selective to phthalic anhydride and more selective to carbon oxides.