The title complex, [Co(C(8)H(8)O(5))(H(2)O)(3)]·H(2)O, was synthesized by reaction of cobalt acetate with 7-oxabicyclo-[2.2.1]heptane-2,3-dicarb-oxy-lic anhydride (norcantharidin) in aqueous solution. In the mol-ecule, the Co(II) atom is six-coordinated in a distorted octa-hedral environment, binding to the bridging O atom of the bicyclo-heptane unit, to two O atoms from monodentate carboxyl-ate groups and to three water O atoms. The crystal structure is stabilized by several O-H⋯O hydrogen-bonding inter-actions involving both the coordinated and uncoordinated water mol-ecules as donors and the carboxyl-ate O atoms of neighbouring mol-ecules as acceptors.