Highly ordered arrays of boron nitride nanotubes (BN-NTs) were prepared for the first time by combining a polymer thermolysis route and a template process. The strategy involves four steps, i.e., synthesis of a liquid polymeric borazine, liquid-phase infiltration of an alumina membrane, thermolysis at 1200 °C under nitrogen of the polymer confined in the 200 nm ordered nanochannels, and template etching to generate BN-NTs arrays supported by a BN sheet. Their crystallinity was controlled through further high-temperature treatments. The thin multiwall BN-NTs displaying dimensions corresponding to the pore size were characterized by electron microscopies and electron energy loss spectroscopy. It was demonstrated that the formation of nanotubes was governed by evaporation of low molecular weight species during the initial steps of the thermolysis, causing loss of nanowire integrity, while a thin film remained and covered the pore walls as a result of the high surface energy of the alumina mold.