In this study, the electrospinning technique was applied to fabricate biocompatible membranes composed of PLLA (Poly-L-lactic acid) and chitosan. With high porosity and interconnected structure, the electrospun membranes were suitable scaffolds for cell or tissue growth. In preparations, injection rate, polymer concentration and applied voltage were varied to investigate their effects on electrospun fibers. The morphology of the electrospun membranes were observed by scanning electron microscopy (SEM). The microphotography indicated that the structures including bead, bead-in-string and nanofibers with different diameters would be controlled by adjusting the above variables. The diameter of strings is about 50 nm and the diameter of beads is ranged from 400 nm to 2 pm, depending on preparation conditions. There was the critical range in the above parameters for the formation of homogeneous nanofibers. Outside the critical range, the bead-on-a-string structures became significant instead. From in vitro experiments, the biocompatibility of electrospun membranes was analyzed by culturing osteoblastic cells with electrospun membranes and dense films. When the osteoblastic cells are cultured with nano-fibrous membranes, the cell density was higher and the secretion of fibril was more significant compared with the cells cultured on dense films. The results indicated that the biocompatibility of PLLA and chitosan would be improved by changing their topography from smooth surface into nano-scaled structures. It manifested the potential of electrospinning technique for biomedical applications.