The structures and energies of BH5 and the transition state for the hydrogen scrambling have been studied using recently developed multicoefficient correlated quantum mechanical methods (MCCMs). We have obtained the dissociation energies between 5.76 and 6.15 kcal/mol, and the barrier heights between 5.44 and 5.83 kcal/mol, which agree very well with the previous results at the CCSD(T)/TZ(3d1f1g,2p1d) level. We have also calculated the potential energy curves for the dissociation of BH5 to BH3 and H-2. The lower levels of theory were unable to plot correct potential curves, whereas the MCCM methods give very good potential energy curves and requires much less computing resources than the CCSD(T)/TZ(3d1f1g,2p1d) level.