Collagen sponges (COL-S) are used as scaffolds to support osteoblasts and stimulate bone repair because of their flexibility, biocompatibility, and biodegradability. In this study, we added fibrin networks to COL-S scaffolds by using a fibrinogen (FNG) cross-linking reaction and evaluated the proliferation, differentiation, and adhesion of MG-63 cells on these scaffolds. The fibrin network that formed in COL-S with various concentrations of FNG was characterized with regard to morphology, porosity, and water-uptake ability. Successful fibrin network formation was observed by scanning electron microscopy (SEM). As the FNG concentration increased, network formation increased, but porosity and water-uptake ability were slightly reduced at high FNG concentrations. An MTS assay, DNA content assay, live/dead fluorescence assay, and SEM imaging showed that MG-63 cells attached and spread on COL-S and COL-S/FNG scaffolds, particularly on scaffolds modified using FNG. In addition, alkaline phosphatase (ALP) activity was significantly increased in cells cultured on scaffolds modified using 10, 40, and 80 mg/mL FNG. Thus, the addition of a fibrin network could increase the biocompatibility of COL-S for bone regeneration. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 101A: 2661–2666, 2013.