Objective:RANKL is a key mediator in the process of osteoclast formation. This membrane-bound protein is a member of the tumor necrosis factor super-family, the purpose of the present study was to assess the level of (RANKL) in samples of gOingival crevicular fluid in insulin dependent diabetes mellitus Patient suffering from chronic periodontitis and to compare it with chronic periodontitis patients and healthy controls. Subjects and Methods: This study was conducted on 45 subjects divided into 15 individual with healthy periodontium and 15 patients suffering from chronic periodontitis 15 patient suffering from both chronic periodontitis and IDDM diagnosed by random blood glucose level >200mg / dl, with the presence of the classical symptoms of IDDM. Clinical recordings (GI, PI, PD, CAL) were scored from each participant in the study. Gingival crevicular fluid samples were obtained from each patient included in the present study from 2 selected sites. RANKL) was measured in the GCF samples by using Enzyme-linked Immuno sorbent Assay Kit. Results: When comparing RANKL level in GCF in control and the two patients groups it revealed that IDDM group showed the statistically significantly highest mean RANKL level. This was followed by chronic periodontitis group. Control group showed the statistically significantly lowest mean RANKL level. Conclusion: The significant increase of GCF level of RANKL play an important role in periodontal breakdown in IDDM.