Oxidative status is attributed to endothelial dysfunction and might be one of the key mechanisms of endothelial dysfunction in acromegaly. In this study, we aimed to investigate the effect of acromegaly on superoxide dismutase (SOD) and total antioxidant capacity (TAC) levels, and the possible influence of human manganese superoxide dismutase (MnSOD) polymorphism on these levels. 51 acromegaly patients and 57 age and sex matched healthy subjects were recruited to the study in Bezmialem Vakif University Hospital between 2011 and 2014. The median SOD and TAC levels were 42.7 (33- 60) pg/mL, and 1,313.7 (155-1,902) mu M in acromegaly; and 46.3 (38-95) pg/mL, and 1,607.3 (195- 1,981) mu M in healthy subjects (p < 0.001, p < 0.001). SOD levels were decreased in controlled and uncontrolled patients compared to healthy subjects (p = 0.05 and p = 0.002, respectively). Controlled and uncontrolled acromegaly displayed significantly decreased levels of TAC compared to healthy subjects (p < 0.05 and p < 0.001, respectively). SOD levels were not associated with MnSOD polymorphisms in acromegaly. In conclusion, this study showed that acromegaly was associated with decreased levels of SOD and TAC, and controlling the disease activity could not adequately improve these levels.