Purpose: Histomorphometry and microhardness measurements were performed after Ti6Al4V implantation in cancellous and cortical bone of healthy and ovariectomized animals to determine characterization of the bone-biomaterial interface in osteopenic bone. Materials and Methods: Nine ovariectomized and 9 sham-aged rats were used. Four months later, nails were implanted in the distal femurs, and the animals were sacrificed after 8 weeks. Moreover, 3 ovariectomized and 3 sham-aged sheep were used. Twenty-four months later, screws were implanted in the tibial diaphyses and the animals were sacrificed after 12 weeks. Results: Histomorphometry showed the development of osteopenia in both trabecular and cortical bone, and revealed a significant decrease in the osseointegration rate in osteopenic versus sham-aged animals for both trabecular (Affinity Index: -18.6%, P .001) and cortical bone (Affinity Index: -23.5%, P .005; Bone Ingrowth: -9%, P .05). At the interfaces of the shamaged animals in both trabecular and cortical bone, a decrease of bone microhardness was observed in comparison with preexisting bone (trabecular: -9.8%, P .0005; cortical: -19.3%, P .0005). In case of osteopenia, this decrease was even more extensive (trabecular: -15.5%, P .0005; cortical: -24.7%, P .0005). Discussion: The present data suggest that bone formation around Ti6Al4V was not associated with complete bone maturation, even in healthy animals. In case of osteopenia, both bone formation and maturation were delayed. Conclusion: These results apparently demonstrate the utility of investigating biomaterials in osteopenic bone and the importance of careful evaluation of the healing rate and bone maturation degree around implanted biomaterials. Keywords: bone-biomaterial interface, implant, microhardness, osseointegration, osteoporosis, titanium alloy