By first-principles calculations, we study the layer number (n) dependent structural evolution, electronic and magnetic properties of two-dimensional bare and semi-hydrogenated (1 1 1)-oriented cubic boron nitride (c-BN) nanosheets. After energy optimization, there is a threshold of n = 7 for maintaining the cubic phase of the bare BN nanosheets. The hydrogenation on either B-end or N-end surface sites would be helpful for stabilizing the c-BN nanosheets with small n, and the structural relaxations on both two outermost surface sides are asymmetric due to different electronegativity between B and N atoms. The bare nanosheets are ferrimagnetic metallic and further turn into ferrimagnetic semiconductor after semi-hydrogenation. (C) 2014 Elsevier B.V. All rights reserved.