The use of electrospun fibrous matrices as substrates for cell/tissue culture has usually been confined to those consisting of smooth fibers. Here, we demonstrated that in vitro responses of mouse-calvaria-derived preosteoblastic cells (MC3T3-E1) that had been cultured on electrospun fibrous substrates made from blend solutions of 50/50 w/w poly(e-caprolactone) (PCL) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) of varying concentrations, ranging from 4 to 14 wt 96, depended strongly on the topography of the individual fibers. As the concentration of the blend solutions increased from 4 to 14 wt %, the topography of the individual fibers changed from discrete beads/smooth fibers to beaded fibers/smooth fibers and finally to smooth fibers, and the average diameter of the individual, smooth fibers increased from similar to 0.4 to similar to 18 mu m. The results clearly showed that MC3T3-E1 preferred the smooth hydrophilic surface of the fibrous substrate from 10 wt % PCL/PHBV solution because the cells appeared to attach, proliferate, and differentiate on the surface of this substrate particularly well.