Developing polymer-based oil/water separation membranes has emerged as a promising approach for wastewater, and fabrication of environmental-friendly separation membranes is becoming a vital issue for sustainable development. Currently, the application of degradable polyesters for oil/water separation is severely limited due to their inferior resistance to various solvents. Herein, we report a new kind of separation membrane of degradable aliphatic polyester based on extended-chain crystals. Though significant improvements in the crystalline structure, including crystallinity and thermodynamic stability, the polyester membranes gain outstanding solvent resistance, maintaining their structural integrity even after prolonged immersion in diverse solvents for up to 100 days. Meanwhile, the hydrophobic and lipophilic characteristic of aliphatic polyester is well inherited in the separation membrane, imparting exceptional wettability to various solvents. Consequently, the extended-chain crystal porous membranes exhibit excellent flux performance and good separation efficiency for solvent and water mixtures and emulsions. In addition, the extended-chain crystal structure gives the membrane outstanding mechanical properties. This work provides the first membrane application report of extended-chain crystal in degradable aliphatic polyester and reveals the potential of extended-chain crystal materials to deliver superior performance and extensive application.