The widespread use of liquid polymers may pollute water, causing grave environmental problems and even various human diseases. The separation of a mixture of a liquid polymer and water is extremely important in research, but the high viscosity, low fluidity, and high adhesion performance of liquid polymers make this task highly challenging. In this paper, we propose a novel strategy for separating a polymer/water mixture wherein porous underwater superpolymphobic micro/nanostructures are used for the first time. Femtosecond laser (fsL) processing is used to form micro/nanoscale surface structures on a stainless steel mesh (SSM), resulting in excellent repellence (underwater superpolymphobicity) to various liquid polymer droplets in water. The laser-induced underwater superpolymphobicity is very stable even though the SSM suffers from different damage treatments (e.g., sandpaper abrasion, acid or alkali solutions corrosion, UV light irradiation, and tape peeling). The underwater superpolymphobicity is ascribed to an underwater Cassie contact state between the underwater liquid polymer and the surface microstructure of the laser-treated SSM. We demonstrate that the underwater superpolymphobic SSM can be effectively and repeatedly used to separate liquid polymer/water mixtures with a high separation efficiency of 99.0% and a high separation flux of 4.45 x 10(5) L m(-2)h(-1). The mixtures of water and different polymers are successfully separated. Such a separation strategy can potentially alleviate pollution from liquid polymer discharge, recycle waste polymer resources, and be applied in polymer production and manufacturing. (C) 2020 Elsevier Inc. All rights reserved.