We perform self-consistent ab-initio calculations to study the structural and electronic properties of zinc blende ZnS, ZnO and their alloy. The full-potential muffin-tin orbitals (FP-LMTO) method was employed within density functional theory (DFT) based on local density Approximation (LDA), and generalized gradient approximation (GGA). We analyze composition effect on lattice constants, bulk modulus, band gap and effective mass of the electron. Using the approach of Zunger and coworkers, the microscopic origins of band gap bowing have been detailed and explained. Discussions will be given in comparison with results obtained with other available theoretical and experimental results.
 K. Iwata, P. Fons, A. Yamada, H. Shibata, K. Matsubara, K. Nakahara, T. Takasu and S. Niki, “Bandgap Engineer ing of ZnO Using Se,” Physica Status Solidi (b), Vol. 229, No. 2, 2002, pp. 887-890. doi:10.1002/1521-3951(200201)229:2<887::AID-PSSB887>3.0.CO;2-G
 S. Savrasov and D. Savrasov, “Full-Potential Linear-Muffin-Tin-Orbital Method for Calculating Total Energies and Forces,” Physical Review B, Vol. 46, No. 19, 1992, pp. 12181-12195. doi:10.1103/PhysRevB.46.12181
 J. P. Perdew and Y. Wang, “Accurate and Simple Analytic Representation of the Electron-Gas Correlation Energy,” Physical Review B, Vol. 45, No. 13, 1992, pp. 13244-13249. doi:10.1103/PhysRevB.45.13244
 Z. Charifi, F. El Haj Hassan, H. Baaziz, S. Khosravizadeh, S. J. Hashemifar and H. Akbarzadeh, “Structural and Electronic Properties of the Wide-Gap Zn1?xMgxS, Zn1?xMgxSe and Zn1?xMgxTe Ternary Alloys,” Journal of Physics: Condensed Matter, Vol. 17, No. 44, 2005, pp. 7077-7088. doi:10.1088/0953-8984/17/44/001
 M. Ameri, D. Rached, M. Rabah, F. El Haj Hassan, R. Khenata and M. Doui-Aici, “First Principles Study of Structural and Electronic Properties of BexZn1–xS and BexZn1–xTe Alloys,” Physica Status Solidi (B), Vol. 245, No. 1, 2006, pp. 106-113. doi:10.1002/pssb.200743128
 H. Baaziz, Z. Charifi, F. El Haj Hassan, S. J. Hashemifar, and H. Akbarzadeh, “FP-LAPW Investigations of Zn1-xBexS, Zn1-xBexSe and Zn1-xBexTe Ternary Alloys,” Physica Status Solidi (B), Vol. 243, No. 6, 2006, p. 1296.
 Y. Z. Zhu, G. D. Chen and H. G. Ye, “Electronic Structure and Phase Stability of MgO, ZnO, CdO, and Related Ternary Alloys,” Physical Review B, Vol. 77, No. 24, 2008. doi:10.1103/PhysRevB.77.245209
 D. Maouche, F. S. Saoud and L. Louail, “Dependence of Structural Properties of ZnO on High Pressure,” Materials Chemistry and Physics, Vol. 106, No. 1, 2007, pp. 11 15. doi:10.1016/j.matchemphys.2007.05.029
 A. S. Mohammadi, S. M. Baizaee and H. Salehi, “Density Functional Approach to Study Electronic Structure of ZnO Single Crystal,” World Applied Sciences Journal, Vol. 14, No. 10, 2011, pp. 1530-1536.
 H.-L. Shi and Y. Duan, “Band-Gap Bowing and P-Type Doping of (Zn, Mg, Be)O Wide-Gap Semiconductor Alloys: A First-Principles Study,” The European Physical Journal B , Vol. 66, No. 4, 2008, pp. 439-444. doi:10.1140/epjb/e2008-00448-6
 B. Amrani, I. Chiboub, S. Hiadsi, T. Benmessabih and N. Hamdadou, “Structural and Electronic Properties of ZnO under High Pressures,” Solid State Communications, Vol. 137, No. 7, 2006, pp. 395-399. doi:10.1016/j.ssc.2005.12.020
 S.-K. Kim, S.-Y. Jeong and C.-R. Cho, “Structural Reconstruction of Hexagonal to Cubic ZnO Films on Pt/Ti/SiO2/Si Substrate by Annealing,” Applied Physics Letters, Vol. 82, No. 4, 2003, p. 562. doi:10.1063/1.1536253
 H. Y. Wang, J. Cao, X. Y. Huang and J. M. Huang, “Pressure Dependence of Elastic and Dynamicalproperties of Zinc-Blende ZnS and ZnSefrom First Principle Calculation,” Condensed Matter Physics, Vol. 15, No 1, 2012, pp. 1-10.
 S.-G. Lee and K. J. Chang, “First-Principles Study of the Structural Properties of MgS-, MgSe-, ZnS-, and ZnSe Based Superlattices,” Physical Review B, Vol. 52, No. 3, 1995, pp. 1918-1925. doi:10.1103/PhysRevB.52.1918
 S. Zh. Karazhanov, P. Ravindrana, A. Kjekhus, H. Fjellvag, U. Grossner and B. G. Svensson, “Electronic Structure and Band Parameters for ZnX (X = O, S, Se, Te),” Journal of Crystal Growth, Vol. 287, No. 1, 2006, pp. 162-168. doi:10.1016/j.jcrysgro.2005.10.061
 M. Oshikiri and F. Aryasetiawan, “Band Gaps and Quasiparticle Energy Calculations on ZnO, ZnS, and ZnSe in the Zinc-Blende Structure by the GW Approximation,” Physical Review B, Vol. 60, No. 15, 1999, pp. 10754 10757. doi:10.1103/PhysRevB.60.10754
 H. Kukimoto, S. Shionoya, T. Koda and T. Hioki, “Infrared Absorption Due to Donor States in ZnS Crystals,” Journal of Physics and Chemistry of Solids, Vol. 29, No. 6, 1968, pp. 935-944. doi:10.1016/0022-3697(68)90228-X