In this work, polydopamine-coated electrospun polystyrene (PS) nanofibrous mats were successfully prepared by simply immersing the PS mats into dopamine alkaline Tris buffer solution for 24 h. The successful growth of polydopamine (Pdop) was confirmed with X-ray photoelectron spectroscopy (XPS). The thickness of the Pdop layer was about 20 nm observed by transmission electron microscope (TEM). The wetting behavior was changed tremendously into superhydrophilicity. Combining the unique characteristics of Pdop as active secondary reaction sites and electrospun mat as a flexible porous support, this hierarchically structured nanofibrous mat can serve as a useful platform for developing porous functional membranes. As demonstrated, oil/water separation and molecule gating membranes were fabricated by using the Michael reaction of Pdop coating with undecanethiol (UT) or 11-mercaptoundecanoic acid (MUA), respectively. As an oil/water separation membrane, the long alkyl chains of UT anchored on the membrane surface increased the contact angle (CA) of water distinctly, and water was blockaded completely while oil smoothly passed through the membrane. Similarly, a molecule gating membrane was constructed based on the pH-induced deprotonation of the carboxyl group of MUA, and its permeation selectivity was confirmed by cyclic voltammetry (CV) with an electrochemical probe. Moreover, the reductive property of the Pdop coating was also utilized to facilely introduce various metal nanoparticles into membrane systems for potential applications, for example, a silver nanoparticle-decorated membrane can be used as an effective antibacterial film as confirmed by the modified Kirby-Bauer method. All performed experiments demonstrate that polydopamine-coated nanofibrous mats can serve as a versatile platform for producing porous functional membranes.