Thermal processes involved in the decomposition course of hydrated ytterbium acetate (Yb(CH3COO)(3). 4H(2)O) and oxalate (Yb-2(C2O4)(3). 6H(2)O) up to 900 degrees C, in atmosphere of air, were monitored by non-isothermal gravimetry and differential thermal analyses. The gaseous decomposition products were identified by gas mass spectroscopy. Intermediates and final solid products were characterized by X-ray and scanning electron microscopy. The results showed that Yb-acetate dehydrates in four steps and decomposes to Yb2O3 at 560 degrees C, through four non-crystalline unstable intermediates. For Yb-oxalate, the dehydration occurs in three steps. The anhydrous oxalate is thermally unstable and immediately decomposes to Yb2O3 at 600 degrees C through two unstable intermediates. The crystalline oxide obtained from the acetate contains large pores in comparison to that oxide obtained from oxalate as indicated from SEM results. The volatile decomposition products from the acetate are water vapor, acetic acid, ketene, acetone and methane.