Disclosed is an emulsion formed using, as an emulsifier, 0.01 to 30 parts by weight of a perfluoroalkylethyl phosphonic acid salt represented by the general formula: C n F 2n+1 CH 2 CH 2 P(O)(OM 1 )(OM 2 ) [III] (M 1 : a hydrogen atom, ammonium salt, or organic amine salt, M 2 : an ammonium salt or organic amine salt, n: 1 to 6), based on 100 parts by weight of a perfluoropolyether oil represented by the general formula: RfO(C 3 F 6 O) p (C 2 F 4 O) q (CF 2 O) r Rf [I] (Rf and Rf: C 1 -C 5 perfluoroalkyl groups, p+q+r: 2 to 200) or the general formula: F(CF 2 CF 2 CF 2 O) n CF 2 CF 3 [II] (n: 2 to 100), or a perfluorocarbon compound. In spite of using, as an emulsifier, a compound having a perfluoroalkyl group containing 6 or less carbon atoms, which is said to have low bioaccumulation potential, the emulsion exhibits excellent emulsification stability, and therefore can be effectively used as a surface-treating agent, such as a. mold-releasing agent.
