Recent studies showed that the fibroblast growth factor 21 (FGF-21) and angiotensin-converting enzyme 2 (ACE2)/Angiotensin 1-7 (Ang 1-7)/Mas axis of the renin-angiotensin system counteract to the negative role of Ang II in various disease. In this study, we examined FGF-21, ACE2, Ang (1-7), and Ang II in obesity and its change after bariatric surgery. We prospectively enrolled obese patient (n=12) who performed bariatric surgery and age-sex matched healthy volunteers (HVs) (n=12 each). Serum FGF-21, Ang II, ACE2, and Ang (1-7) levels were measured by enzyme-linked immunosorbent assay kits. We measured also FGF-21, Ang II, ACE2, and Ang (1-7) 6 months after bariatric surgery in obese patients. FGF-21, Ang II and ACE2 levels were significantly higher in obese patients compared with HVs (p = 0.034, < 0.001, and p = 0.020, respectively) and decreased after bariatric surgery (p = 0.002, 0.005, and 0.020, respectively) (Figure 1). There was no significant difference in Ang (1-7) levels between obese patients and HVs (p = 0.887). Weight reduction surgery did not change  Ang (1-7) levels in patients with obesity (p = 0.480). However, changes in Ang (1-7) levels were positively correlated with changes in body mass index (BMI) after surgery (R2 = 0.580, p = 0.048) (Figure 2). FGF-21 and ACE2 were upregulated in patients with obesity and they are reduced after bariatric surgery. A decrease in BMI after bariatric surgery was associated with the decrease in Ang (1-7).