||The optical band gap bowing of eighteen III–V compound alloys containing boron is calculated by means of a recent phenomenological model [M. Ferhat, Phys. Status Solidi b 241 (2004) R38]. The optical band gap bowing is found to be strong for the all studied III–V boron alloys. In particular, we find that BNSb shows an important optical band gap bowing of 19.78 eV. Parallel to this, we also introduce ab initio pseudopotential plane wave calculations with large relaxed supercells to check the validity of our phenomenological model for BNSb. This gives an optical bowing of 21.19 eV, in fairly good agreement with the model used. Results suggest that the III–V boron alloys are characterized by a strong competition between the volume deformation Click to view the MathML source, charge transfer Click to view the MathML source, and structural relaxation Click to view the MathML source effects. For the common cation alloys Click to view the MathML sourcedominates Click to view the MathML source, and Click to view the MathML source is relatively weak; whereas for the common anion alloys, the structural effect (Click to view the MathML source and Click to view the MathML source) appears to control the total optical band gap bowing.