In this study, we quantitatively analyzed the affinity of cell adhesion to aligned nanofibers composed of composites of poly(glycolic acid) (PGA) and collagen. Electrospun composite fibers were fabricated at various PGA/collagen weight mixing ratio (7, 18, 40, 67, and 86%) to generate fibers that ranged in diameter from 10 mum to 500 nm. Scanning electron microscopy (SEM) observation revealed that the PGA/collagen fibers were long and uniformly aligned, irrespective of the PGA/collagen weight mixing ratio. In addition, it was observed that a significantly higher number of NIH3T3 fibroblasts adhered to nanofibers with smaller diameters in comparison to fibers with larger diameters. The highest affinity of cell adhesion was observed in the PGA/collagen fibers with diameter of 500 nm and PGA/collagen weight mixing ratio of 40%. Furthermore, the adherent cells were more elongated on fibers with smaller diameters. Thus, based on the results here, PGA/collagen composite fibers are suitable for tissue culture studies and provide an attractive material for tissue engineering applications.