Large-scale synthesis of BN multi-walled nanotube (MWNT) ropes from C MWNT templates was carried out. A mixture of B2O3 and MoO3 was used as an oxidizing agent during a chemical reaction involving C MWNT oxidation in a flowing nitrogen atmosphere at 1773 K. Encapsulation of Mo-based clusters into the BN MWNTs was simultaneously achieved. The morphology, atomic structure and chemical composition of MWNTs synthesized at 1773 K with and without MoO3 promoter were compared by means of high-resolution transmission electron microscopy and electron energy loss spectroscopy. A striking increase in BN MWNT yield and self-assemblage of tubes into ropes were discovered under MoO3-promoted synthesis.