Lens-shaped microstructures on solid surfaces are important for a variety of applications, such as enhanced water harvesting, super-resolution imaging, and antireflection. Here the formation of polymeric microlenses with tunable contact angles based on an Ouzo effect is reported. In this process, water is added into a binary toluene/ethanol solution in contact with a polystyrene (PS) thin film. The dilution by water leads to spontaneous formation of toluene microdroplets due to the reduced solubility of toluene in the ternary liquid mixture (i.e., the Ouzo effect). PS in the thin film is dissolved into the toluene droplets. However, the droplets containing PS and toluene are not stable against dissolution, and eventually toluene dissolved into the surrounding ternary mixture. PS in the droplets is left on the substrate, forming microlenses on the supporting glass substrate. The size and density of PS lenses are influenced by PS film thickness and toluene concentration in the surrounding liquid. The contact angle of PS microlens could be varied through a thermal reshaping method. As demonstration for potential applications, the results show that the as-prepared microlenses can improve the spatial resolution of a standard upright optical microscope.