Diabetes mellitus (DM) is a common disease occurring worldwide. Patients with DM are at an increased risk of losing their teeth compared to other individuals. DM increases the risk and severity of chronic inflammatory periodontal diseases, in which, bone resorption is found to occur. Chronic inflammation contributes to the development of DM and DM-associated complications. Hyperglycemia is a hallmark of DM and may contribute to sustained inflammation by increasing the levels of proinflammatory cytokines. However, the mechanisms by which bone-related complications develop in DM after stimulation by the Porphyromonas gingivalis lipopolysaccharide (P. gingivalis LPS) remain unknown. Results of studies performed to understand the effect of high glucose concentrations on the functions of osteoblasts are contradictory because some have suggested a subsequent increase (although others have suggested a decrease) in the rate of the biomineralization process. Therefore, we evaluated the effect of high glucose levels on the biomineralization and inflammation markers in a human osteoblastic cell line, after stimulation with LPS from P. gingivalis. We treated cells with glucose at concentrations 5.5, 8.0, 12 and 24 mM after stimulation with P. gingivalis LPS (1.0 mg/ml) and determined its effects on cell proliferation, alkaline phosphatase (ALP) activity, osteocalcin (OCN) production, calcium deposition, inflammatory cytokines, and osteogenic cytokines. Results demonstrated that high concentrations of glucose increased cell proliferation, but the ALP activity decreased at concentrations of 12 and 24 mM. Additionally, OCN production and Calcium (Ca) deposition decreased at 24 mM. The levels of inflammatory cytokines (IL-1β, IL-6 and IL-8) decreased at 8.0 and 12 mM. However, the amounts of Runx2 increased significantly in the presence of 12 mM glucose, but decreased beyond this concentration. High glucose concentration decreased hard tissue formation after stimulation by P. gingivalis LPS. Understanding the effect of glucose on osteoblast differentiation and calcium deposition might provide a better understanding of the development and prevention of periodontitis associated with diabetes.