The solution-mediated synthesis and crystal structure of 1,1-dimethylhydrazinium tetraphoshonoatotrizincate, (C2H9N2)2[Zn3(HPO3)4], are described. The anionic [Zn3(HPO3)4]2− framework is built up from alternating ZnO4 tetrahedra and HPO3 pseudo-pyramids to generate a three-dimensional 4,3-net encapsulating the C2H9N2 + cations. The organic cations, which are protonated at their central N atoms, occupy pores delineated by large 16-membered polyhedral rings and interact with the framework by way of N—H...O hydrogen bonds and possible C—H...O interactions. One of the zinc ions lies on a crystallographic twofold rotation axis and all the other atoms lie on general positions. The crystal studied was found to be rotationally twinned about the [001] axis in reciprocal space in a 0.585 (5):0.415 (5) ratio.