Purpose: Diabetes mellitus has been shown to delay osseointegration of titanium dental implants. This study tested the hypothesis that serum derived from diabetes negatively affects osteoblast adhesion to polystyrene and titanium surfaces, partly through the presence of advanced glycation end products (AGEs). Materials and Methods: Twenty-four Sprague- Dawley rats were divided into three groups: normoglycemic control, streptozotocin-induced diabetic group, and diabetic group treated with the AGE inhibitor aminoguanidine. Polystyrene or titanium disks were preincubated in serum derived from each group. Human osteoblasts transfected with green fluorescent protein (GFP) were cultured, and the number of adherent osteoblasts was quantified. High-pressure liquid chromatography (HPLC) was used to fractionate eluates, which were further characterized by western blot with AGE antibody and adhesion assays. In parallel, sera derived from healthy patients, patients with controlled diabetes, and patients with uncontrolled diabetes were utilized for osteoblast adhesion assay and western blot. Results: Diabetic serum significantly reduced the number of adherent osteoblast and osteoblast aggregates on titanium disks, whereas aminoguanidine-treated serum rescued the effect of diabetes on the number of adherent osteoblast aggregates. Fractionated diabetic serum revealed distinct AGE bands at ~100 kDa and 44 kDa, whereas healthy serum did not express any. In human serum samples, both controlled and uncontrolled diabetes led to a significant reduction in the number of adherent osteoblasts on polystyrene and titanium surfaces compared with normoglycemic serum. This correlated with presence of AGEs in western blot in diabetic but not in healthy serum. Conclusion: Osteoblast adhesion on the titanium surface was greatly reduced by the exposure of serum derived from diabetic rats or humans. Recovery of osteoblast aggregates by aminoguanidine treatment suggests that AGEs played a role in this negative effect. The correlating presence of AGEs from the fractionated sera of diabetic rats or humans and impaired osteoblast adhesion on the titanium surface further supports this role. Keywords: bone healing, dental implant, diabetes mellitus, hyperglycemia, metabolism, osseointegration, osteoblast, streptozotocin, wound healing