The presence of leptin (OB) and soluble OB receptor (s-OB-R) in gingival tissue extract and gingival crevicular fluid has led the studies investigating the relationship between OB and periodontal diseases. This study aims to investigate the levels of OB and s-OB-R in serum and their presence in gingiva of healthy controls (HC), gingivitis (G), aggressive periodontitis (AP), and chronic periodontitis (CP) patients; and whether correlations exist between clinical and serum parameters, OB and s-OB-R. Seventy-seven subjects [HC (n = 20), G (n = 20), CP (n = 21), and AP (n = 16)] were included in this study. After the clinical periodontal parameter recordings and venous blood sampling, gingival tissues obtained. Serum parameters' levels determined with enzyme linked immune sorbent assay; and OB and OB-R in gingiva immunohistochemically. No significant differences were observed regarding the serum parameters [high sensitivity C-reactive protein (hs-CRP), lipids, OB, and s-OB-R] when the groups were compared (P > 0.0125). The serum OB has positive correlations with hs-CRP in the G group (P < 0.05), and s-OB-R has presented significant negative correlations with BOP in HC group (P < 0.05), with hs-CRP in G (P < 0.05) and AP groups (P < 0.05). The positive correlations were observed between the serum OB and HDL and body mass index in the CP group (P < 0.05). In all of the tissue samples of all groups, there was positive OB and OB-R immunoreactivity in the gingival epithelium. The gingival tissues contain both OB and OB-R. The serum levels of OB and s-OB-R do not vary between patients and with different periodontal conditions.