The present invention relates to a method for preparing polyols of formula (I) ##STR00001## R.sub.1 being H or an alkyl group, R being especially an alkyl group, A.sub.1, being an alkylene radical and R.sub.3, are being especially a group -A.sub.2-OY, A.sub.2 being an alkylene radical and Y being especially H, said method especially comprising a step of epoxidation of a compound of formula ##STR00002## R.sub.1 being H or an alkyl group, A.sub.t being defined as above in formula (I) and R.sub.4 being especially a group -A.sub.2-OY.sub.1, A.sub.2 being defined as above in formula (I) and Y.sub.1 being especially H, in order to obtain a compound of formula ##STR00003## A.sub.1 being defined as above, R.sub.1 being H or an alkyl group and R.sub.5 being especially a group of formula -A.sub.2-OY.sub.2, A.sub.2 being as defined above in formula (I) and Y.sub.2 being especially H.