First-principles calculations were carried out to predict the electronic and optical properties of PtS2 monolayer. We interpreted that the band gaps of monolayer (ML) PtS2 can be tuned continuously via strain engineering. In this thesis, both tensile and shear strains were investigated. It was testified that mechanical strains reduce the band gap of ML PtS2 causing an indirect-to-direct band gap transition. These transitions, in turn, significantly depend on the type of applied strain. The optical properties were calculated and a clear red shift was observed with the increasing strain.