[en] Uncertainty of Doppler reactivity is theoretically formulated and then uncertainties of self-shielding factor f(T) and its temperature gradient α due to errors of resonance parameters were evaluated from NJOY output. In the course of evaluation, serious investigation on numerical differentiation method was made for so-called two or three-point model, significance of figure of NJOY output and acceptable digits for computers. The f(T) and α uncertainties based on JENDL-3.3 covariance file were evaluated by using computer code system ERRORF newly developed for present work as a modular code system consisting of NJOY for effective cross section and f-factor calculations, REPCHANGE for parameter change and FTOALPHA for covariance calculation. Sensitivity analysis was made for ²³⁵U, ²³⁸U, ²³⁹Pu and ²⁴⁰Pu based on JAERI Fast set-3 70 group structure. Importance of off-diagonal terms was emphasized in the uncertainty evaluation. Resultant sensitivity coefficients are provided for the uncertainty evaluation of Doppler reactivity. (author)