An alkoxido-bridged tetranuclear Dy(iii) complex, [Dy4(H3L)2(OAc)6]·2EtOH {, H6L = 1,3-bis[tris(hydroxymethyl)methylamino]propane}, has been solvothermally synthesized and characterized. An X-ray crystallographic study revealed that complex possesses a novel "parallelogram" [Dy4(OCH2-)4] core, and a new binding mode η(3):η(3):η(1):η(1):η(1):η(2):μ(4) of the Bis-tris propane ligand was observed. Magnetic investigations indicated that it is a single-molecule magnet (SMM), showing two distinct magnetic relaxation processes with the energy barriers of 44 K and 107 K, respectively. Such a two-step magnetic relaxation process could be well described by the sum of two modified Debye functions.