The thermal decomposition reactions of vanadyl and vanadium acetoacetonates in dry nitrogen have been thoroughly studied. Thermal processes occurring throughout the decomposition range (100-500 degrees C) were monitored by means of TG, DTA and IR spectroscopic analysis of the gaseous products. These processes were characterized on the basis of the solid product analyses using X-ray diffractometry and IR spectroscopy. The results showed that VO(C5H7O2)(2) had completely decomposed to V2O3 at 325 degrees C through the intermediates VO(CH3COO)(C5H7O2) at 290 degrees C, VO(CH3COO)(2) at 300 degrees C and V2O(CO3)(2) at 305 degrees C. In contrast, V(C5H7O2)(3) decomposed via the acetate at 280 degrees C and the carbonate at 292 degrees C as intermediates. The carbonate decomposed immediately to give V2O5 at 305 degrees C. Part of the V2O5 underwent a reduction process through an endothermic effect at 325 degrees C. The ultimate solid products at 400 degrees C were V2O3 and V2O5. Gas phase products included propyne, acetone, carbon oxides, methane and isobutene. Methane and isobutene resulted from interfacial reaction involving the initial product (acetone).