Development of new heterogeneous base catalysts for Knoevenagel condensation reactions is critical for practical applications. Herein, we demonstrate that carbon doped hexagonal boron nitride (BCN) exhibits a high catalytic activity for Knoevenagel condensation of benzaldehyde with malononitrile, producing benzylidene malononitrile under mild reaction conditions. An 81.9% conversion can be achieved over BCN after 15 min reaction time, which is 1.8 times with respect to hexagonal boron nitride (h-BN) and 27 times over C3N4. Moreover, the BCN catalyst could be easily separated and recycled for several runs without obvious deactivation. Experimental results, spectroscopic characterizations, combined with first-principle calculations, suggest the reaction likely follows a dissociative adsorption mechanism on the oxygen terminated BCN edge. The C atoms doping plays a vital role in promoting the desorption of the intermediates. This study can open up a new avenue for the Knoevenagel condensation reaction with metal-free catalysis.