Background: Bone-graft substitutes are a frequently employed method for the clinical reconstruction of osseous bone defects, and research on synthetic biomaterials is currently ongoing. Absorbable hemostatic gelatin sponge and hydroxyapatite–chitosan nanocomposites (nHAp/CS) have gained popularity in recent years because of their inherent characteristics: osteogenesis, osteoconductivity, osteoinductivity, biodegradability, and biocompatibility. Aim: The aim of the study was to evaluate the effectiveness of 1) a gelatin-based hemostatic sponge (Surgispon) and 2) a combination of a weight ratio of 75/25 nHAp/CS composite with a Surgispon for osteogenic potential in the treatment of full-thickness segmental osseous defects in the radius of rabbits. Methods: The 18 New Zealand rabbits had 10-mm-induced segmental diaphyseal defects of the left limb radius and were randomly allocated into three groups: group I left the defects untreated (control group), group II used a Surgispon, and group III had a weight ratio of 75/25 nHAp/CS composite wrapped with a Surgispon. Quantitative evaluation of the bone repair at the defect site in each group (n = 6), radiographic, gross, computed tomography (CT), and histopathological examinations were performed at 6 weeks (n = 3) and 12 weeks (n = 3) postoperatively. Results: The quantitative statistical analysis of various evaluation methods at 6 weeks post-implantation demonstrated that there was no statistically significant difference between the groups (p > 0.05). The statistically significant differences (p < 0.05) between groups I and II, while groups I and III, were evident 12 weeks postoperatively. Conclusion: The findings of the radiographic, macroscopic, CT, and histopathological analyses firmly demonstrate that the combination of a 75/25 weight ratio composite of nHAp/CS with Surgispon is more effective than Surgispon alone in its ability to significantly increase bone formation. This could provide a prospective option for treating segmental bone defects