The optimized structures of studied compounds 23-28 are non planner with the two phenyl at C3 and C9 are out of the molecular plane of thiazolo[3,2-a]pyridine as indicated from a dihedral angles of 710 and 1160 respectively, using DFT-B3LYP method with 6-311G(d,p) as basis set. The natural bonding orbital (NBO) analysis of the parent molecule 23 have been analyzed in terms of the hybridization of each bond, natural charges, bonding and antibonding orbital's, and second order perturbation energy (E(2)). The calculated EHOMO and ELUMO energies of the studied compounds can be used to explain the extent of charge transfer in the molecule and to calculate the global properties; the chemical hardness (η), global softness (S), electrophilicity (ω), and electronegativity (χ). The effect of substituent's of different strengths on the geometry, energetic and nonlinear optical properties are analyzed and discussed. The NLO parameters: static dipole moment (µ), polarizability (α), anisotropy polarizability (Δα), and first order hyperpolarizability (βtot), of the studied compounds have been calculated at the same level of theory and compared with the proto type Para-Nitro-Aniline (PNA). The results of (βtot) promising electrical properties. The 3D plots of the molecular electrostatic potential (MEP) for some selected compounds were investigated and describing the electrophilic and nucleophilic sites. The biological activity of the studied compounds was tested against gram positive, gram negative and Fungi. A correlation between energetic, global properties and biological activity were investigated and discussed.