Objective: Amino-terminal propeptide of C-type natriuretic peptide (NTproCNP) is a synthesis product of C-type natriuretic peptide (CNP). In this study, plasma levels of NTproCNP were compared before and after exercise in healthy young subjects who are physically active (PA) or not physically active (NPA). Methods: The study was carried on PA group (n=10) who defined the exercise duration more than 2.5 hours per week for at least one year and NPA group (n=10) whose exercise duration was lower than 1.5 hours per week. The level of maximal oxygen consumption was determined. Wingate exercise test was applied on the following day. Plasma NTproCNP levels were measured before the exercise and at the 1st, 5th and 30th minute after the exercise. Results: Exercise duration of physically active group was reported as 11.3±5.0 hours per week. Basal NTproCNP levels of the groups were found to be comparable. NTproCNP levels in the 5th minute (0.93±0.23 pmol/L; p<0.05) and in the 30th minute (0.77±0.21 pmol/L p<0.05) after exercise were higher than the levels before exercise (0.64±0.29 pmol/L) in PA group. Additionally, the plasma levels of NTproCNP after 5th minute of exercise were higher in PA group (0.93±0.23 pmol/L) than NPA group (0.74±0.16 pmol/L, p<0.05). Conclusion: Being physically active may be a fact affecting the secretion of CNP, which plays a protective role in endothelium, following exercise. (Anatolian J Cardiol 2015; 15: 97-102)