Solvothermal reaction of yttrium chloride hydrate and trimethoxyborane in 1,4-butanediol in the presence of airlines at 315 degrees C directly yielded YBO3 crystals having flower-like morphology (particle size; 3-8 mu m). The crystal growth toward the c axis was inhibited by adsorption of amines on the ab plane, and plate-like crystals were formed. The luminescence chromaticity of Y0.9Eu0.1BO3 samples synthesized by solvothermal reaction was different from that prepared by solid-state reaction; samples synthesized by the solvothermal reaction exhibited larger relative intensity ratio of the emission at 580 nm to that at 610 nm than samples prepared by the solid-state reaction.