The title compound, [Ni(C 10 H 8 O 4 )(C 16 H 20 N 4 )(H 2 O) 2 ] n , contains Ni II cations octa-hedrally surrounded within an [O 4 N 2 ] coordination set. The cations are linked by 4-(carb-oxy-eth-yl)benzoate (ceb) and 1,4-bis-(pyridin-4-ylmeth-yl)piperazine (bpmp) ligands into tri-periodic diamondoid ( dia ) networks. The fivefold inter-penetrated dia networks are held into the crystal structure by means of O-H⋯O hydrogen bonding between bound water mol-ecules and unligated carboxyl-ate O atoms of the ceb ligands.