Extremely asymmetric wettability, high wetting selectivity, instantaneous superwetting behaviors (low transmembrane resistance), and superior resistance to chemicals and solvents are needed for Janus membranes for switchable oil/water separation. However, it is still challenging to obtain Janus membranes with such properties. In this study, a surface with metastable hydrophobicity is constructed on one side of the chemically stable superhydrophilic TiO2@PPS membrane by adjusting the hydrophobization depth and the morphology of the hydrophobic layer via a water-oil interfacial grafting. The prepared Janus membrane exhibits a high water contact angle difference of ∼150° between its two surfaces with maintaining the superior penetrability of the original membrane, which makes it capable to separate both oil-in-water and water-in-oil emulsions with high fluxes and accuracy. The separation efficiency is higher than 98% for the separation of the two kinds of emulsions. The fluxes of the surfactant-free toluene-in-water and water-in-toluene emulsions are up to 6.4 × 102 and 9.5 × 102 L m-2 h-1, respectively. Furthermore, the Janus membrane exhibits desirable antifouling performance and reusability during usage.