Monolayer black phosphorus is a potential anode material for rechargeable ion batteries. In this work, the effects of intrinsic defects including mono-vacancy (MV), di-vacancy, and Stone-Wales (SW) defects on the adsorption and diffusion of sodium on monolayer black phosphorus were investigated using first-principles calculations. The adsorption energies for sodium on monolayer black phosphorus are in the range of -1.80 to -0.56 eV, which is lower than the value of -0.48 eV for sodium adsorbed on pristine monolayer phosphorus. This indicates that these defects can enhance the adsorption of sodium on monolayer black phosphorus. The diffusivity of sodium on monolayer phosphorus with SW and MV defects is 2.35 x 10(-4)-3.36 x 10(-6) cm(2)/s, and 7.38 x 10(-5)-1.48 x 10(-9) cm(2)/s, respectively. Although these values are smaller than that of the pristine monolayer phosphorus at 7.38 x 10(-5) cm(2)/s, defects are inevitably introduced during these fabrication processes. These diffusivity values are reasonable for defective monolayer phosphorus used as an effective anode for sodium ion batteries. (c) 2017 Elsevier B.V. All rights reserved.