A dysprosium-carboxylate coordination polymer, {[Dy-2(2,2'-bpdc)(3)(e-urea)(H2O)](e-urea)}(n) (I) (2,2'-bpdc(2-) = 2,2'-biphenyldicarboxylate and e-urea = ethyleneurea), has been synthesized using a deep-eutectic solvent of choline chloride/e-urea. Four Dy3+ ions are linked by the carboxylate oxygen atoms of the 2,2'-bpdc(2-) ligands to form a linear Dy-4 unit, which is further linked by the carboxylate groups of the 2,2'-bpdc(2-) ligands to give a rare example of one-dimensional chain based on the linear Dy-4 secondary building units. Detailed static and dynamic magnetic analysis of 1 revealed that 1 exhibits a slow magnetic relaxation behavior.