Pure poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and zinc oxide (ZnO)/PHBV composite nanofibers were fabricated by an electrospinning method. ZnO nanoparticles (NPs) with a diameter of about 10-20 nm were doped in the PHBV fibers and no dispersion agent was utilized. Both pure PHBV and composite electrospun fibers were smooth and uniform. ZnO NPs did not affect the basic crystalline structure of electrospun PHBV fibers. The well dispersion of NPs was attributed to the interaction of hydrogen bonds between -OH groups on the surface of ZnO and C=O groups in the PHBV. ZnO NPs were not nucleating or modifying agents but retarding agents for crystallization in the polymer matrix. The crystallinity and crystallization rate was lowered by adding ZnO NPs. The well dispersion of ZnO NPs in the electrospun nanofibers was confirmed by TEM characterization. A hypothesis was developed to interpret the influence of ZnO NPs on the crystalline behavior of electrospun PHBV fibers. (C) 2010 Elsevier Ltd. All rights reserved.