The magnesium(II) hydrotris(1-pyrazolyl)borate, Mg[BH(pz)3]2, complex has been, for the first time, tested as a precursor for the metal organic chemical vapor deposition (MOCVD) of borate phase thin films. The thermal analyses of this source reveal high volatility and good thermal stability with a low residue left despite its relatively high melting point. In particular, the compound has been successfully applied to the MOCVD fabrication of Mg2B2O5 films, and therefore it represents a suited and reliable single source precursor of borate phases. Mg[BH(pz)3]2 provides constant evaporation rates even for very long deposition times and, hence, highly homogeneous films of carefully controlled thickness.