Materials innovation plays an essential role to address the increasing demands of gaseous chlorine from anodic chlorine evolution reaction (CER) in chlor-alkali electrolysis. In this study, two-dimensional (2D) semiconducting group-VA monolayers were theoretically screened for the electrochemical CER by means of the density functional theory (DFT) method. Our results reveal the monolayered β-arsenene has the ultralow thermodynamic overpotential of 0.068 V for CER, which is close to that of the commercial Ru/Ir-based dimensionally stable anode (DSA) of 0.08 V @ 10 mA cm−2 and 0.13 V from experiments and theory, respectively. The change of CER pathways via Cl* intermediate on 2D β-arsenene also efficiently suppresses the parasitical oxygen gas production because of a high theoretical oxygen evolution reaction (OER) overpotential of 1.95 V. Our findings may therefore expand the scope of the electrocatalysts design for CER by using emerging 2D materials.