Polymeric membranes, compared with their inorganic counterparts, usually suffer from insufficient solvent resistance and thermal stability. In this study, an organic solvent-resistant thermally stable polymeric micro-filtration membrane is prepared with a self-crosslinkable polybenzoxazine as a precursor. The obtained membranes have pore sizes of approximately 3.4 mu m and superior antiswelling stability in organic solvents; thus, they exhibit excellent performance in terms of size-selective particle separation inorganic phases. The membranes are also effective in the gravity-driven separation of surfactant-stabilized water-in-oil emulsions. The water contents of the filtrate oil phases are close to the natural solubility of water in the solvents; for example, a water content of 350 ppm, which is comparable to the water solubility in toluene (330 ppm), has been found in the filtrate toluene from water-in-toluene emulsions. Moreover, the membrane demonstrates pH-induced changes in oil and water selectivity in oil-water separations. When treated with a strong base solution, the oil-selective membrane becomes water-selective and exhibits favorable performance in terms of separating organic solvents from surfactant-stabilized oil-in-water emulsions. These features effectively extend the application scope of the prepared membrane for oil-water separations.