Porous fibers are advantageous for filtration systems, drug delivery systems, and in the field of tissue engineering, in comparison to their non-porous counterparts. In this study, we developed a facile technique including two steps to generate poly(3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV) porous fibers with a controllable pore size. An electrospinning technique was employed to obtain five types of PHBV/poly(ethylene oxide) (PEO)-blended fibers (PHBV:PEO=9:1, 8:2, 7:3, 6:4, 5:5) with PEO as the porogen. PEO was leached out by simulated body fluid (SBF) and water, respectively. The pore morphology and calcium deposition of the resulting fibers were compared to those formed on film through the SEM-EDX analysis. It was revealed that pore size and number increased with increasing PEO percentage in the fiber or film. The pore size on the films (at micrometer scale) was much larger than that of nanofibers, which was in the range of 70-120nm. The simultaneous removal of PEO and deposition of calcium phosphate through SBF buffer enhanced synergistically both the pore formation and mineral deposition. The different phase separation mechanisms explain the different pore morphologies in the film and the nanofibers. The cellular experimental results show that fibers with nanometer-scale pores and minerals can enhance the proliferation of bone marrow-derived mesenchymal stem cells.