In the title coordination polymer, {(CH6N3)[Y(CHO2)4]} n , the yttrium(III) ion is coordinated by one O,O-bidentate formate ion and six μ2 bridging formate ions, generating a square-anti-prismatic YO8 coordination polyhedron. The bridging formate ions connect the metal ions into an anionic, three-dimensional network. Charge compensation is provided by guanidinium ions, which inter-act with the framework by way of N-H⋯O hydrogen bonds. The guanidine molecules reside in porous channels of 3.612 by 8.189 Å, when considering the van der Waals radii of the nearest atoms (looking down the a-axis).