A new trimethyltin(IV) coordination polymer, [Sn(CH3)3(C7H8O2P)], has been prepared by treatment of methylphenylphosphinic acid and trimethyltin chloride with sodium ethoxide in methanol. In the solid state, the title compound adopts an infinite one-dimensional polymeric chain structure with each SnIV atom adopting a distorted trigonal–bipyramidal geometry.