The optimization of a kinetic mechanism of the pyrolysis of ethyl iodide was carried out based on data obtained from reflected shock wave experiments with H-ARAS and I-ARAS detection. The analysis took into account also the measurements of Michael et al. (Chem. Phys. Lett. 2000, 319, 99–106) and Vasileiadis and Benson (Int. J. Chem. Kinet. 1997, 29, 915–925) of the reaction H2 + I = H + HI. The following Arrhenius parameters were determined for the temperature range 950–1400 K and the pressure range 1–2 bar: C2H5I → C2H5 + I: log10(A) = 13.53, E/R = 24,472 K; C2H5I → C2H4 + HI: log10(A) = 13.67, E/R = 27,168 K; H + HI → H2 + I: log10(A) = 13.82, E/R = 491 K; C2H5I + H →C2H5 + HI: log10(A) = 15.00, E/R = 2593 K (the units of A are cm3, mol, s). The joint covariance matrix of the optimized Arrhenius parameters was also determined. This covariance matrix was converted to the temperature-dependent uncertainty parameters f of the rate coefficients and also to the temperature-dependent correlation coefficients between pairs of rate coefficients. Each fitted rate coefficient was determined with much lower uncertainty compared to the estimated uncertainty of the data available in the literature.