The slow crystallization kinetics of model networks consisting of end-linked poly(tetrahydrofuran) (PTHF) was investigated as a function of the prepolymer molecular weight, M(n). The crystallization half times, t(1/2), estimated by both differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS), were in good agreement with each other. It was found that t(1/2) was very sensitive to M(n), ranging from 40 to 400 min when crystallized at 15 degrees C. This strongly indicates depression of the capability of crystallization by the introduction of cross-links. The role of cross-links on isothermal crystallization is discussed from both kinetic and thermodynamic points of view.