[en] Unfolding process has been applied to neutron spectra derivation of many measurement methods. Previously, many types of unfolding techniques have been developed. Many codes of them, however, cannot calculate uncertainty propagation, and thus uncertainty characteristics comparison of some codes has not been investigated. To solve this problem, we have developed an uncertainty estimation method based on Monte-Carlo technique. Moreover, we have investigated characteristics of uncertainty propagation of two unfolding codes, GRAVEL and MAXED. For demonstration, we measured a double-differential thick-target neutron yield (DDTTNY) of the C(d,n) reaction induced by 20-MeV deuterons with the multiple-foil activation method at Cyclotron and Radioisotope Center, Tohoku University. The measured data were analyzed by GRAVEL and MAXED, and their uncertainty propagation was estimated by using the present method. As a result, we found that the uncertainty of DDTTNY has neutron energy dependence, and the dependency trend is different between GRAVEL and MAXED codes. (author)