Melting behavior of poly(tetrahydrofuran)-s (PTHF) and their blend with different molecular masses has been studied by TM-DSC. PTHF and their blend show two endothermic peaks on their curve. The melting peak temperatures T m1 and T m2, entropy of fusion ΔS f1 and ΔS f2, and mean relaxation time for melting τf1 and τf2 have been estimated, and their dependence on the molecular mass has been examined. Plots of Tm1 to the reciprocal of their molecular mass fit a simple equation (T m=a-b/M n). Plots of T m2 to their molecular mass also fit the equation with different factors. There seems to be a boundary around molecular mass 1200 in the molecular mass dependence of ΔS fand τf. Effect of blending appeared on the τf and the non-reversing heat flow.