A novel method for determining the minimum crystallizable sequence length, ζ * , of the semicrystalline copolymers was proposed recently. By applying it to several semicrystalline copolymer systems, the general applicability of the method was tested. The value of ζ * was found to be dependent on the crystallization conditions and the size of the comonomer unit. The rationality of the present method comparing with that of Burfield's was demonstrated.