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) 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 guests readily bind to the dimeric Pt building blocks of the internal cavities via electrostatic and specific Pt···Pt 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 species over other metal ions in water upon simple filtration.