The present study aimed to evaluate the activity of prolidase in controlled acromegaly patients and its association with oxidative stress. 25 acromegalic patients in remission who were followed in our outpatient clinic and 31 healthy controls were enrolled in the study. Serum growth hormone (GH), insulin-like growth factor 1 (IGF-1), total antioxidative status (TAS), total oxidative stress (TOS), total free sulfhydryl (-SH), paraoxonase (PON), arylesterase (ARE), lipid hydroperoxide (LOOH) and prolidase activity levels were measured. Percent ratio of TOS to TAS level was accepted as oxidative stress index (OSI). Serum prolidase activity, TOS, OSI, and LOOH levels were significantly higher in acromegaly patients compared to the healthy control group (p < 0.001, p = 0.001, p < 0.001, and p < 0.001, respectively). SH levels were significantly lower in the acromegaly patients compared to the healthy control group (p = 0.002). Prolidase activity were positively correlated with TOS, OSI, LOOH and negatively correlated with -SH in patients with acromegaly (r = 0.471, p < 0.001; r = 0.527, p < 0.001; r = 0.717, p < 0.001; r = -0.516, p < 0.001, respectively). These associations were confirmed in the multiple regression analysis (R-2 = 0.502, p < 0.001). In conclusion, serum prolidase activity and oxidative stress levels were high in controlled acromegaly patients. These results suggest that extracellular matrix changes continue eventhough the disease is controlled, and elevated oxidative stress is involved in the increased prolidase activity in acromegaly patients.