Tellurite glasses are of great importance in fiber optic amplifying applications and as laser hosts. Comparing with silicate, borate and phosphate glasses, tellurite glasses have superior properties, such as low-phonon energy, high refractive index, high dielectric constant, good corrosion resistance, thermal and chemical stability. TeO(2) is the main but the conditional glass former; therefore, addition of a secondary component, such as heavy metal oxides, increases the glass forming ability. The present study aims to investigate the phase equilibria in the TeO(2) - WO(3) system. Three different compositions, (1-x)TeO(2)-xWO(3) (X = 0.10, 0.15, 0.20 in molar ratio) were prepared. The samples were heated in a platinum crucible for 30 minutes at 750 degrees C, then were quenched and crushed. TG/DTA, XRD and SEM techniques were used to investigate the samples.