beta-MoO3 was successfully synthesized through a simple evaporation of a molybdic acid solution prepared by a cation exchange of an aqueous solution of Na(2)MoO(4)(.)2H(2)O. The key was an addition of a small amount of nitric acid before the evaporation. Heating the dried molybdic acid at 573 K in oxygen resulted in a formation of a bright yellow powder, which was confirmed to be beta-MoO3 free from alpha-MoO3 by XRD and Raman spectroscopy.