Proton magnetic resonance spectra of beryllium hydroxide β-Be(OH)2 and products of its thermal decomposition are studied at room temperature and 123 K. It is shown, based on these spectra and differential thermal analysis and x-ray diffractometry data, that, heated to above 500 K, β-Be(OH)2 decomposes into a finely dispersed BeO and H2O to convert finally to an amorphous beryllium oxyhydroxide. At above 600 K, a crystalline BeO is formed involving dehydration of the finely dispersed BeO and amorphous oxyhydroxide phase.