The compounds of Co(II) and Ni(II), incorporating ligands with different sets of donor atoms, remain attractive for research because of their usefulness and relevance, such as biological activity, theoretical studies, magnetic properties, catalysis, etc [1]. Rhodanine-3-acetic acid (2-(4-oxo-2- thioxothiazolidin-3-yl)acetic acid) (HRaa) has become an interesting important heterocyclic moiety in chemistry owing to its wide spectrum of biological activities through different mechanisms of action. Due to various possibilities of chemical modification, rhodanine-based compounds were considered as a privileged scaffold in drug discovery. Thus, the combination of Co(II) and Ni(II) salts with HRaa resulted in two isostructural compounds with formula [Co(Raa)2(H2O)4] (1) and [Ni(Raa)2(H2O)4] (2) that crystallize in the monoclinic P21/c and P21/n space groups. Their crystal structures have been determined by single crystal X-ray diffraction. The asymmetric units of 1 and 2 comprise ½ of centrosymmetric complexes. In these coordination mononuclear compounds metal centers are six-coordinated by O6 set of donor atoms of four water molecules and two monodeprotonated Raa- (Fig. 1). Each ligand Raa- in 1 and 2 acts as monodentate donor to one metal atom. The Co-O bond distances in coordination polyhedra of 1 range from 2.087(2) to 2.141(2) Å and Ni-O bond distances of 2 range from 2.042(5) to 2.114(5) Å.  The coordinated water molecules in 1 and 2 are involved in the formation of intra- and intermolecular hydrogen bonds. One O(w)-H...O(carb) hydrogen bond stabilized complex and multiple O(w)-H...O hydrogen bonds link the complexes into a H-bonded layer (Fig. 2). Weak S...S interactions stabilize the three-dimensional architecture in crystals. Biological properties are in progress.