A self-scaling rheology-based technique was developed to determine the molecular weight (MW) and molecular weight distribution (MWD) of ethylene-tetrafluoroethylene alternating copolymer (ETFE). The self-scaling technique makes determining MW and MWD with isolated completely rheological method possible. Moreover, the two key parameters (the plateau modulus and zero-shear viscosity) were obtained by more robust numerical technique, which let determining MW and MWD via rheological method initiated by Tuminello [Macromolecules 1993, 26, 499] being building on more robust and rigid basis. Our case overcomes the shortage of Tuminello's method and gives more practical and simply mean to analyze the MW scale and MWD in the production and application of ETFE. It is found that the peak MW of a ETFE (commercial grade: EP541) is 1.73 x 105 g/mol, the MWD curve is a pattern with a slightly raised shoulder at high-molecular mass end, and a high peak on the median and the polydispersity is broad (the polydispersity index is near to 10.3). The wide polydispersity indicates the commercial ETFE combining good processability of relative lower MW molecules with physical properties of high MW ones. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012