In this study, the structural and electronic properties of semiconductor Tl (x) Al1-x P alloys were derived from minimum total energy by using Density Functional Theory with Local Density Approximation. A 16 atom supercell was used to model the ternary Tl (x) Al1-x P alloys. The lattice constant, electronic band gap energies and bowing parameters was examined. The lattice constant of the Tl (x) Al1-x P alloys comply well with Vegard's law. Also, the polynomial equation of concentration dependent electronic band gap energy of the Tl (x) Al1-x P is E-g (x) = 2.02693x (3) - 2.17819x (2) - 1.15118x + 1.29644 (eV). Electronic band gap bowing parameters vary depending on the Thallium concentration value. It was concluded that the average bowing parameter of Tl (x) Al1-x P alloys was b = 1.1649 eV.