Abstract: Polyurethanes with the ureidopyrimidone side groud were synthesized from 4,4′-diphenylmethane diisocyanate and polytetramethylene glycol(PTMG), incorporating 2-methyl-2-UPy(2-ureido-4［1H］-pyrimidone)-1,3-propanediol as chain extender, of which the structure was confirmed by FT-IR and 1H-NMR. Results of tensile test demonstrated that the mechanical properties of polyurethanes were greatly improved by introducing UPy group in the side chain. In dynamic mechanical thermal analysis, with the increasing of the content of UPy, the glass transition temperature increased correspondingly, whereas the peak value of tan δ decreased. In the wide frequency field, with the increasing of the content of UPy, the influence of frequency to peak value of tan δ and storage modulus (E′) would lead the movement of peak value of tan δ to low frequency, peak intensity decreased, tan δ and E′ increased.