In recent years, a variety of fibrous bioactive bioceramic-polymer composite scaffolds were made through electrospinning and their usefulness for bone tissue engineering was investigated. In this study, nanospheres of carbonated hydroxyapatite (CHA), which is a proven osteoconductive and biodegradable bioceramic, were synthesized using a nanoemulsion process and relatively high amounts of CHA nanospheres were successfully incorporated into electrospun poly(hydroxybutyrate-co- hydroxyvalerate) (PHBV) fibers with the aid of an ultrasonic power source. The biological evaluation of electrospun fibrous PHBV scaffolds and CHA/PHBV nanocomposite scaffolds were conducted through in vitro cell culture using the human osteoblast cell-line SaOS-2. Although both types of scaffolds supported the proliferation and spreading of SaOS-2 cells, the CHA/PHBV scaffolds caused significantly higher expression of alkaline phosphatase (ALP) activity of SaOS-2 cells than the PHBV scaffolds after 14 days of cell culture, indicating the potential of fibrous CHA/PHBV nanocomposite scaffolds for bone tissue regeneration applications.