The glycothermal reaction of the rare earth (RE) acetates with trimethoxyborane (RE/B = 1) at 315 degrees C for 2 h yielded REBO3 for Tm, Yb and Y. For Gd-Er, REBO3 was contaminated with amorphous products. Mixtures of RE(OAc)O, REBO3 and amorphous products were obtained for Sm and Eu, while only RE(OAc)(2)(OH) was obtained for La. The space group of the REBO3 crystal obtained from Sm-Er and Y was P6(3)/m, and mixture of REBO3 crystals with P6(3)/m and R (3) over barc were obtained for Tm and Yb. Prolonged reaction time (6 h) yielded REBO3 without contamination of the amorphous product or RE(OAc)O for Eu-Yb and Y. For the reaction of yttrium acetate and trimethoxyborane with Y/B ratio of 1/3-3/1 for 2 h, YBO3 was only the binary oxide detected. The YBO3 particles were spheroidal with a diameter of 1 mu m. The selected area electron diffraction of a whole particle indicated that the each particle is a "single crystal" of YBO3 grown from one nucleus.