A method for the production of an aqueous dispersion of a water insoluble N-substituted N',N'-alkylene urea having the general formula I: ##STR1## wherein R.sup.1 denotes alkyl having 6 to 20 carbon atoms, phenyl or ##STR2## in case of m=1, or R.sup.1 denotes alkylene having 6 to 20 carbon atoms, phenylene or ##STR3## in case of m=2, where X denotes H, CH.sub.3 or OCH.sub.3 and n is 0 or 1, R.sup.2 denotes H or CH.sub.3, R.sup.3 denotes H, CH.sub.3 or C.sub.2 H.sub.5 and R.sup.4 denotes H or CH.sub.3, by the reaction of an alkylene imine having 2 to 4 carbon atoms with an isocyanate represented by the general formula II:R-NCO (II)wherein R denotes an alkyl having 6 to 20 carbon atoms, ##STR4## wherein X and n are the same as above in the presence of at least one surface active agent selected from the group consisting of anionic surface active agents and nonionic surface active agents under vigorous stirring.