The applied uniaxial stress can break the original symmetry of a material, providing an experimentally feasible way to alter material properties. Here, we explore the effects of uniaxial stress along an arbitrary direction on mechanical and electronic properties of phosphorene, showing the enhancement of inherent anisotropy. Basic physical quantities including Young's modulus, Poisson's ratio, band gap, and effective carrier masses under external stress are all computed from first principles using density functional theory, while the final results are presented in compact analytical forms.