The density functional theory technique based on the Full Potential Linear Augmented Plane Wave (FP-LAPW) method is used to investigate the structural, electronic, and optical properties of AgGaS2 under different values of axial strain. The structural parameters are in good accordance with experimental ones. Furthermore, the Tran-Blaha modi?ed Becke-Johnson (TB-mBJ) potential method is used to achieve the desired band structure, which verifies the experimental results. It is observed that when tensile strain (0%, +3%, +6%, +9%) is applied, the bandgap reduces from 2.253 eV to 1.645 eV and when compressive strain (0%, -3%, -6%, - 9%) is applied, band gap increases from 2.253 eV to 2.9331 eV. Axial strain enhances the absorption, reflection and refractive index, which compromises the transparent performance in visible region. Due to high absorption coefficient and close to the optimal bandgap, AgGaS ₂ is a suitable material for solar cell and light emitting diodes and related applications. The main focus of the study is to tune bandgap and optical properties of AgGaS2 by using biaxial tension.