Replacement of extensive local bone loss especially in revision joint arthroplasty and spine fusion is a significant clinical challenge. Allograft and autograft have been considered as gold standards for bone replacement. However, there are several disadvantages such as donor site pain, bacterial contamination, and non union as well as the potential risk of disease transmission. Hydroxyapatite and collagen composites (HA/Collagen) have the potential in mimicking and replacing skeletal bones. This study attempted to determine the effects of newly developed HA/Collagen-composites with and without bone marrow aspirate (BMA) on enhancement of bone implant fixation. Method: Titanium alloy implants were inserted into bilateral femoral condyles of eight skeletally mature sheep, four implants per sheep. The implant had a circumferential gap of 2 mm. The gap was filled with: HA/Collagen; HA/Collagen-BMA; autograft or allograft. Allograft was served as the control group. The observation period was 5 weeks. The sheep were euthanized and both femurs were harvested. A push-out mechanical test and histological analysis were performed. Results: No significant differences were seen in the mechanical properties and histomorphometry between autograft and allograft groups. The implants in both the HA/Collagen and HA/Collagen-BMA groups were mostly surrounded by fibrous tissue. Thus, mechanical testing of these samples was impossible. The histomorphometry results showed significantly more new bone and bone ongrowth in the allograft and autograft group compared with the HA/Collagen and HA/Collagen-BMA groups, but no significant difference between HA/Collagen and HA/Collagen-BMA. Conclusion: Autograft and allograft have similar effect on fixation of bone implants. HA/Collagen composite with or without BMA has no effect on the early fixation of bone implants in this sheep model. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2012.