Recovering heavy and precious metals from wastewater is both economically and environmentally attractive. However, a challenge still remains in how to realize the highly selective removal and recovery of a particular metal of interest, such as platinum. Here we experimentally demonstrate a two-dimensional (2D) supramolecular polymer that can serve as a host for the highly selective capture of anionic platinum(II) (Pt-II) species including its metal-organic complexes and water-soluble ions. This host polymer possesses a 2D honeycomb-like nanostructure noncovalently bridged by cationic alkynylplatinum(II) terpyridine dimers. Anionic Pt-II guests readily bind to the dimeric Pt-II building blocks of the internal cavities via electrostatic and specific Pt-II center dot center dot center dot Pt-II interactions. Such unique host-guest interactions have endowed thin membranes comprising highly oriented supramolecular polymers with a versatile ability to selectively recognize and adsorb anionic Pt-II species over other metal ions in water upon simple filtration.