The hydrothermal reaction of cobalt(II) chloride with trimesate (3,5-dicarboxybenzoate) ions in aqueous solution gives the novel title complex, [Co(C9H5O6)(2)(H2O)(4)]. The Co-II ion lies on an inversion centre and is octahedrally coordinated to two trimesate anions and four water molecules. Hydrogen bonds ensure the three-dimensional architecture of the structure.