The capillary extrusion property of ethylene–tetrafluoroethylene copolymer (ETFE) is evaluated. It is found that ETFE shows several types of flow instabilities. The shark-skin failure is observed over the first critical shear stress 7.9×104Pa. Then, the slip-stick instability is detected at 1.8×105Pa, which corresponds to the critical stress of the slippage at the die wall, evaluated by the Mooney method. Moreover, gross wavy melt fracture appears at high out-put rate condition. It is interesting to note that quasi-stable flow region; so-called “super-extrusion”, is observed between slip-stick and wavy melt fracture regions. Because of the steady slippage, ETFE can be extruded at a high out-put rate condition without surface roughness and distortion of extrudates.