Reaction F2 + C2H4 → F + C2H3F (1) has been studied using a discharge flow reactor combined with an electron impact ionization mass spectrometer. The reaction rate constant was determined either from kinetics of the reaction product, F-atom, formation or from the kinetics of F2 consumption in excess of C2H4: k1 = (7.94 ± 2.06) × 10−12 exp(−(3867 ± 120)/T) cm3 molecule−1 s−1 at T = 297–833 K. The reaction activation energy, 7.7 ± 0.3 kcal mol−1, is consistent with current theoretical prediction for the reaction barrier height and seems to solve the long-standing problem of the divergence between theory and experiment.