We report the synthesis, crystal structures, and spectral, thermal, and magnetic properties of a family of metal–organic perovskite ABX3, C(NH2)3MII(HCOO)3, in which A=C(NH2)3 is guanidinium, B=M is a divalent metal ion (Mn, Fe, Co, Ni, Cu, or Zn), and X is the formate HCOO−. The compounds could be synthesized by either diffusion or hydrothermal methods from water or water‐rich solutions depending on the metal. The five members (Mn, Fe, Co, Ni, and Zn) are isostructural and crystallize in the orthorhombic space group Pnna, while the Cu member in Pna21. In the perovskite structures, the octahedrally coordinated metal ions are connected by the anti–anti formate bridges, thus forming the anionic NaCl‐type M(HCOO)3− frameworks, with the guanidinium in the nearly cubic cavities of the frameworks. The Jahn–Teller effect of Cu2+ results in a distorted anionic Cu–formate framework that can be regarded as Cu–formate chains through short basal CuO bonds linked by the long axial CuO bonds. These materials show higher thermal stability than other metal–organic perovskite series of AmineHM(HCOO)3 templated by the organic monoammonium cations (AmineH+) as a result of the stronger hydrogen bonding between guanidinium and the formate of the framework. A magnetic study revealed that the five magnetic members (except Zn) display spin‐canted antiferromagnetism, with a Néel temperature of 8.8 (Mn), 10.0 (Fe), 14.2 (Co), 34.2 (Ni), and 4.6 K (Cu). In addition to the general spin‐canted antiferromagnetism, the Fe compound shows two isothermal transformations (a spin‐flop and a spin‐flip to the paramagnetic phase) within 50 kOe. The Co member possesses quite a large canting angle. The Cu member is a magnetic system with low dimensional character and shows slow magnetic relaxation that probably results from the domain dynamics. Nice cubes: A family of metal–organic perovskite salts of C(NH2)3M(HCOO)3 for divalent Mn to Zn were synthesized from water or water‐rich solutions. They possess anionic NaCl‐type frameworks of M(HCOO)3 with guanidinium in the cubic cavities (see figure); the magnetic members show spin‐canted antiferromagnetism.