Abstract In this study, intrinsic mobility of monolayer BC 2 N is investigated by the first-principles calculation. First, it is calculated from deformation potential theory (DPT) based on longitudinal acoustic and optical phonon scatterings. The values from longitudinal acoustic phonon scattering are higher than those from optical phonon scattering, so the mobility from DPT is mainly determined the optical phonon scattering. At 300 K, electron mobility is 3 . 82 × 1 0 2 cm 2 V − 1 s − 1 along zigzag direction, and 3 . 41 × 1 0 1 cm 2 V − 1 s − 1 along armchair direction, while hole mobility is 3 . 48 × 1 0 2 cm 2 V − 1 s − 1 along zigzag direction, and 2 . 63 × 1 0 1 cm 2 V − 1 s − 1 along armchair direction. Then, we investigate the carrier mobility from the electron–phonon coupling (EPC) matrix elements. If the polarization effect is considered in the calculation, the mobility along zigzag direction is reduced to be 58 ∼ 110 cm 2 V − 1 s − 1 for electron, and 41 ∼ 70 cm 2 V − 1 s − 1 for hole. It is found from vibration modes that the longitudinal optical phonon scattering dominates the carrier mobility. Because some empirical models do not consider Frohlich interaction, the mobility is greatly over estimated. In this study, we reveal the factors that affect the mobility and give a more reasonable prediction for the mobility of monolayer BC 2 N .