The electronic and magnetic properties of the boron nitride (BN) sheets with different chemical decoration are investigated using the first-principles plane-wave calculations within density functional theory (DFT). It is demonstrated that bare BN sheets are nonmagnetic semiconductors with wide band gaps, and a metallic–semiconducting–half-metallic transition with a nonmagnetic– magnetic transfer can be realized through chemical decoration. Specifically, BN sheets modified by H with zigzag configuration still behave as semiconductors, while with armchair configuration are metallic. Nevertheless, decorating BN sheets by F or OH with zigzag configuration reveal half-metallic properties, then with armchair configuration present spin-polarized semiconducting characteristics. The results may be of importance in designing BN-based electronic devices for nanoelectronic applications.