Among various rare earth phosphates, CePO4 and LaPO4 were found to catalyze the oxidative dehydrogenation of isobutane to iso-butene at 450-550 degrees C using a feed gas of 75 mol% iso-butane and 5 mol% O-2. As for the phosphates of Y, Pr, Nd, Gd, Er, and Yb, iso-butene was formed with a limited selectivity of 20-40% selectivity, and C3H6 formation and deep oxidation into CO and CO2 were promoted over the same temperature range. Temperature-programmed-desorption spectra of NH3 for CePO4 and LaPO4 consisted of two large desorption peaks with maxima at 100 degrees C and 270 degrees C suggesting that these phosphates have strong acid sites. But the rest of the phosphates have only weak acid sites.Rare earth phosphates have no adsorbed oxygen which can be desorbed up to 550 degrees C. The lattice oxygen of CePO4 and PrPO4 can be reduced at 200 degrees C and that of the rest of the phosphates at about 400 degrees C, The amount of oxygen removed up to 550 degrees C in TPR was smaller than the amount corresponding to a monolayer for all phosphates. Oxygen isotope equilibration experiments over CePO4 and LaPO4 revealed that only surface lattice oxygen can participate in the equilibration at 500 degrees C and 550 degrees C.It can be concluded that acidic character is a key factor in the selective oxidative dehydrogenation of iso-butane over the rare earth phosphate catalysts.