Periodontal bone loss results from bacterial infection and the associated host response. The ligand for the receptor activator of NF-κB (RANKL) induces the differentiation of osteoclasts, resulting in periodontal bone loss. The role of osteocytes in periodontal bone loss was investigated in this study. Transgenic mice expressing RANKL under the control of dentin matrix protein 1 (DMP1) were infected with Porphyromonas gingivalis- Fusobacterium nucleatum bacteria (Pg-Fn) to induce periodontitis, and type 1 diabetes was induced in groups of mice. Control (DMP1Cre−.RANKLf/f) mice with periodontal infection showed increases in bone loss, osteoclast counts, eroded bone surfaces, and RANKL expression compared to experimental (DMP1-Cre+.RANKLf/f) mice. RANKL deletion from osteocytes resulted in less periodontal bone loss. Diabetes enhanced periodontal bone loss in the control mice. The diabetic control (DMP1Cre−.RANKLf/f) mice had more bone loss than the non-diabetic control (DMP1Cre−.RANKLf/f) mice. In the experimental (DMP1-Cre+.RANKLf/f) mice, diabetes had no influence. This study demonstrated, for the first time, the essential role of osteocytes in periodontal bone loss.