Structures of protonated borane-Lewis base complexes H4BX+ (X = NH3, PH3, OH2, SH2, CO) as well as their neutral parents were calculated using ab initio method at the MP2/6-31G** level. All of the monocations H4BX+ are B-H protonated involving hypercoordinate boron with a three-center two-electron (3c-2e) bond. Protonation energies of H3BX to form H4BX+ were calculated with the G2 theory and were found to be highly exothermic. The B-11 NMR chemical shifts of the compounds were also calculated by the GIAO-MP2 method.