First-principles computation is used to examine lattice parameters, energy band gap and optical properties of ZnO under uniaxial strain. The calculation is carried out in uniaxial (c-axis) strain changing in the range from 5% to 5%. The simulations are based upon the Perdew-Burke-Ernzerhof form of generalize gradient approximation within the density functional theory. There is linear variation of lattice constant and linear boarding of energy band gap with uniaxial strain increment. Strain in the c-axis direction has prime contribution in the variation of energy band of ZnO. Absorption coefficient, optical properties comprising dielectric function (real and imaginary) and reflectivity of wurtzite ZnO are deduced. Diminishing of imaginary part of the dielectric function with the increase of uniaxial strain at low energy is observed in calculated results but imaginary part of the dielectric function is observed to increase with increasing uniaxial strain for energy greater than 5.0 eV and a blue shift is appeared in graph. Strained band gap of ZnO is larger than that of unstrained ZnO, which provides the theoretical reference value for the modulation of the band gap of ZnO. © 2020 Polish Academy of Sciences. All rights reserved.