Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB-co-4HB) nanofiber membranes were papered via electrospinning from polymer solution. The electrospinning parameters such as solution concentration, feed rate, applied voltage, collection distance were optimize in order to reduce fiber diameter and distribution. The nanofiber membrane was characterized by SEM, FTIR, DSC, XRD and tensile test. According to SEM results, the averaged diameter and distribution of nanofibers could be reduced down to 454nm and 0.191, respectively. The DSC and XRD results indicated that the crystallization regularity was improved and the range of melting temperature decreased due to the orientation of molecular chains along the fiber axis. The electrospun P3HB-co-4HB nanofiber membranes was flexible but easy broken.