The present invention relates to a composition for reshaping keratin fibers with heat, comprising: (a) at least one organic alkaline agent having a pKa value of from 8.0 to 13.5; and (b) at least one polymeric thickener, (c) at least one organic acidic agent having pKa value of less than 3.5, and/or (d) at least one alkaline agent; wherein the composition has a pH of from 8.0 to 12, preferably from 8.5 to 11.5, and more preferably from 9.0 to 11.0. The composition according to the present invention is preferably a cosmetic composition, for keratin fibers, such as hair, and can be used for a process for reshaping the keratin fibers with heat. The composition according to the present invention can provide the keratin fibers with a sufficient reshaping efficiency such as strong wave intensity of the curled keratin fibers and good usability.