In this study, leptin hormone levels were measured by using the ELISA technique in serum samples taken from 300 Iraqi adults of both sexes, 100 healthy people as a control group, 100 people with only rheumatoid arthritis (RA), and 100 patients with both RA and type 2 diabetes (DM). Then, the relationship between leptin concentration and blood sugar, lipid profile, liver enzymes (Alanine transaminase (ALT), Aspartate transaminase (AST), Alkaline phosphatase (ALP)), and Apolipoprotein E (ApoE) in health, RA, and RA & DM people were investigated. Results show that leptin has an inverse and insignificant relationship with cholesterol, triglyceride, and low-density lipoprotein, while it has a direct and insignificant relationship with high-density lipoprotein. RA & DM patients showed an inverse correlation between leptin and AST. There was no positive or significant correlation for the rest of the enzymes. Regarding the relationship between leptin and liver enzymes, the normal state showed an inverse relationship between leptin and ALT levels, while the rest of the relationships were direct and insignificant. Leptin showed a positive correlation with AST and ALT and a non-significant inverse correlation with ALP in subjects with RA. RA & DM showed an inverse correlation between leptin and AST.