The transition in the malt of FEP copolymer was detected by differential scanning calorimeter and torsional braid analysis techniques．In order to darify the nltture of the transition．the changes of malt viscosity with temperature and shear rate were investigated by capillary rheometer and micro．paraUel type rheometer．The result obtained shows that，theplot of ln n vs．1／T of FEP copolymer at constant shear rateor sheading stress does not show a linear relationship as usually observed in the conventional polymer melt but an ano-malous increase of n，when the temperature incneases above the transition temperature．This rheological behavior is similar to that of low molecular liquid crystal．But no birefrin-gence in the meh can be perceived under crossed polarizing microscope．Based on these ex-perimental facts，a model was presented to explain this transition．