The development of surface microstructure with specific features in electrospun nanofibers has attracted more and more attention in recent years. In this article, a common biological polyester, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was electrospinning into nanofibers with "coral-like" surface microstructure by a conventional-electrospinning setup. The effect of the process parameters on the microstructure in electrospun nanofibers were investigated via a series of experiments. The formation mechanism of this feature structure and cytotoxicity assays of PHBV membrane were also discussed. The water contact angle of the electrospun PHBV membrane was higher than that of the PHBV cast film due to a very-rough fiber surface including porous beads when PHBV was electrospun from the concentration of 4 wt %. Because of special hole shape and size distribution, the physical structure of surface of PHBV electrospun fibers offered it special properties, such as specific-surface area, hydrophilic-hydrophobic properties, adhesion properties of cells and biological substances, etc. The demonstrated method of form coral structure would contribute to the areas such as filtration, sensor, tissue engineering scaffolds, and carriers of drugs or catalysis. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 2867-2874, 2013