Three novel polyoxometalates (POMs) containing [Ni6(μ3-OH)3](9-) and [P2W15O56](12-) units were first made, showing the first hexa-nuclearity transition-metal substituted POMs (TMSPs) based on monomeric lacunary Dawson fragments, which further indicates that the hydrothermal technique can offer an effective way for making new TMSPs through lacunary POM fragments incorporated with high-nuclear TM clusters.