Novel porous quasi single-crystal B-doping BiO2-x (B-BiO2-x) nanosheets were synthesized via a facile hydrothermal method with boric acid (HBO3) as B source. Benefiting from unique microstructure and B doping, as-prepared B-BiO2-x delivered remarkable photocatalytic activity, whose apparent rate constant for the degradation of methyl orange (MO) was 5 times higher than that of BiO2-x. Besides, B-BiO2-x also showed decent photochemical stability. This work presents a new insight into design and synthesis of porous quasi single-crystal photocatalysts.