Abstract: A physical transition T_u in the melt of tetraftuoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) can be detected by torsional braid analysis technique. The crystalline morphologies of the melt-crystallized PFA. also show a significant dependence on the melt temperature round about the transition temperature T_u. When PFA is cooled and crystallized from a temperature in the range of T_u to Tm, the randomly arranged lamella will be obtained, when it is cooled from a temperature above T_u, the spherulitic morphology will be formed; and when it is cooled from a temperature within the transition temperature range T_u, the rodlike morphology will be obtained. The isothermal crystallization rate, measured by DSG, also has a distinct change above and below T_u. But differential scanning calorimetry measurement does not show an endothermic peak occurring at transition temperature interval, so the transition is attributed to the change of chain configuration with the increase of temperature.