A series of Te-Mo-O catalysts were prepared by decomposing (NH4)(4)TeMo6O22 center dot 2H(2)O telluromolybdate under different conditions and tested for the oxidation of isobutane and isobutene. Characterization results (XRD, FTIR, TG, TPR, XPS, and BET) showed that their structure and properties depend on calcination conditions. Catalytic tests showed that molybdenum may be the key element for the activation of isobutane, whereas the selective oxidation of isobutene to methacrolein (MAL) might proceed mainly on the surface of the TeMo-containing crystalline phase. Thus, relatively high selectivities and yields of MAL and methacrylic acid (MAA) can be obtained over these specially designed catalysts.