The thermal processes involved during the decomposition course of hydrated erbium acetate (Er(CH3COO)(3). 4H(2)O) up to 800 degreesC in an atmosphere of static air were monitored by non-isothermal gravimetry and differential thermal analyses. The gaseous decomposition products were identified by IR spectroscopy. Intermediates and final solid products were characterized by IR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that Er acetate dehydrates completely in one step and decomposes to Er2O3 at 590 degreesC through three noncrystalline unstable intermediates. The volatile decomposition products from the acetate are water vapor, acetic acid, ketene and acetone. Er2O3 obtained from ErAc at 800 degreesC has large porous particles with surface area of 55 m(2)/g. Er2O3 obtained catalyzes the decomposition of acetone to give methane and isobutene.