The thermal decomposition of europium (III) acetate tetrahydrate has been studied by thermal analysis, X-ray diffraction, IR, gas chromatography and chemical analysis. The dehydration of tetrahydrate begins at 70°C and two unknown hydrates are produced in the process of the dehydration, which occurs in three steps. Two unknown hydrates are found to be monohydrate and hemihydrate. Anhydrous europium (III) acetate obtained by this study is a new polymorph. The anhydride slowly decomposes to europium (III) oxide carbonate above 280°C, passing through an intermediate compound. Finally, europium (III) oxide is produced. The intermediate compound shows a new X-ray diffraction pattern and is estimated to be EuOCH3COO.