The reaction of rare-earth (RE; Y, Er, and Yb) chloride hydrates in 1,4-butanediol at 300 degrees C for 2 h gave mixtures of RE(OH)(2)Cl and RE2O3.xH(2)O, and the products were composed of irregularly shaped particles. A prolonged reaction (10 h) yielded a mixture of RE(OH)(2)Cl and RE2O3.xH(2)O for Er or Y, but phase-pure RE2O3.xH(2)O was obtained for Yb. The product for Yb comprised needle-shaped single crystals of Yb2O3.xH(2)O with a width of 0.2-0.6 mu m and a length of 5-15 mu m. The Yb2O3.xH(2)O phase decomposed to Yb2O3 at 350 degrees-500 degrees C, preserving the needle-shaped morphology; this was maintained even after calcination at 1100 degrees C. Single crystals of Yb2O3 obtained by the calcination of Yb2O3.xH(2)O at 500 degrees C had very small voids and the voids were enlarged to 35 angstrom in diameter by calcination at 800 degrees C.