The crystal structures of the synthesized superhard diamondlike BC5 have been extensively explored through ab initio evolutionary algorithm. We uncovered seven intriguing low-energy structures all possessing sp3 hybridizations. After examining the dynamical stability, it is found that two Pmma structures (Pmma-1 and Pmma-2) are energetically more preferable. The simulated x-ray diffraction pattern, Raman modes, and Vickers hardness for Pmma-1 and Pmma-2 structures show remarkable agreement with the experimental data. Electronic and electron–phonon coupling calculations reveal that the two Pmma structures are hole conducting and superconducting with critical temperature ∼11–23 K.