Abstract The effects of HCl concentration and temperature on the dissolution of La 2 O 3 in aqueous (HCl–H 2 O), mixed-aqueous (HCl–CH 3 OH–H 2 O) and non-aqueous (HCl–CH 3 OH) solvents have been studied. Increase of methanol in solvents was determined to cause corresponding decreases in conductivity, E SCE , pH values with corresponding increase in E R values and better results were obtained for dissolution in the order non-aqueous>mixed-aqueous>aqueous solvent systems. Increase in dissolution was attributed to the prevention of lanthanum hydroxide precipitation in non-aqueous medium. Lanthanum compounds formed in non-aqueous medium at 25°C were isolated and identified using X-ray diffraction, thermal and chemical analysis methods and the thermal changes observed in these compounds between 25°C and 1100°C were investigated. LaCl 3 · x 1 CH 3 OH and LaCl 3 · x 2 CH 3 OH·3H 2 O ( x 1 + x 2 =2.35) were formed in non-aqueous medium and these compounds were converted into LaCl 3 ·1.14CH 3 OH with complete and partial loss of water and methanol around 165°C, respectively. Methanol was completely removed around 200°C with formation of LaCl 3 and some LaOCl and due to the decomposition of LaCl 3 above 200°C, LaOCl was detected as the only stable phase above 700°C.