Background: Acute rheumatic fever is an immunologically delayed autoimmune sequel of throat infection caused by group A streptococcus. The aim of this study was to evaluate endocan levels in patients with acute rheumatic fever and compare with the control group. Aim: The aim of this study was to evaluate endocan levels in patients with acute rheumatic fever and compare with the control group. Methods: Twenty-three children with acute rheumatic fever (11 men, 12 females; mean age 13 ± 2.7 years; range 5 to 15 years) and a healthy control group of 31 children (16 men, 15 females; mean age 13.8 ± 2.4 years; range 5 to 15 years) were recruited. The sedimentation rate, C-reactive protein, antistreptolysin-O titres, and endocan levels were examined in each group. Results: Before anti-inflammatory therapy, endocan levels in the acute rheumatic fever group were not statistically significant to those in the control group, respectively (200.64 ng/L, 120.71 ng/L, P = 0.208). After anti-inflammatory therapy, endocan levels were significantly higher in the acute rheumatic fever group than in the control group, respectively (260.87 ng/L vs. 120.71 ng/L, P < 0.01). A significant difference was found in endocan levels before and after anti-inflammatory therapy in the group of acute rheumatic fever, respectively (200.64 ng/L vs. 260.87 ng/L, P = 0.033). Endocan levels after anti-inflammatory therapy were statistically higher in the severe carditis group compared to those of the mild carditis group, respectively (344.56 ng/L vs. 191.01 ng/L, P < 0.01). Conclusion: Our study showed that serum endocan levels increased during the subacute phase of acute rheumatic fever. We suggest that serum endocan level can be used as a new biomarker to identify the degree of cardiac involvement in acute rheumatic fever.