Abstract: There is provided a novel perfluorochemical represented by the formula, ##STR1## wherein R.sub.F is a perfluoroalkyl group, a perfluoro alkoxyalkyl group or a perfluoroalkyloxy group, X and X' are same as or different from each other and are a fluorine atom or a perfluoroalkyl group, and Y is a perfluoroalkyloxy group or a perfluoro dialkylamino group, the total number of the carbon atoms contained being an integer of 8 to 11 inclusive. The perfluorochemical is prepared by perfluorinating the corresponding partially fluorinated compound which may have unsaturated hydrocarbon moiety, only with molecular fluorine in a stoichiometric excess amount in an inert solvent.The perfluorochemical is used for preparing a stable emulsion as blood substitutes or perfusion media.