Objective. The aim of this study was to evaluate paraoxonase-1 (PON1) activities and oxidative stress status, and the changes in their levels after total thyroidectomy in patients with papillary thyroid cancer (PTC). Materials and methods. Twenty-five patients with PTC and 27 healthy controls were enrolled in the study. Blood samples were obtained from the PTC patients before and 3 months after the operation. Preoperative and postoperative serum samples from PTC patients and healthy controls were analyzed for paraoxonase (PON), arylesterase (ARE) activities, and lipid hydroperoxide (LOOH) and -SH (total free sulfhydryl) levels. Results. The preoperative PON, ARE and -SH levels of the patients with PTC were significantly lower compared to those of the control group (p = 0.033, p < 0.001, p = 0.002, respectively), while LOOH levels were significantly higher (p < 0.001). The levels of PON and ARE decreased significantly in patients with PTC after the operation (p = 0.038, p = 0.023, respectively), while LOOH and -SH levels remained unchanged (p = 0.117, p = 0.487, respectively). PON and ARE levels showed a positive correlation with -SH (r = 0.211, p = 0.065; r = 0.471, p < 0.001, respectively) and a negative correlation with LOOH (r = -0.391, p < 0.001, r = -0.486, p < 0.001, respectively). Conclusion. Serum PON1 activity is decreased in patients with PTC, and serum PON1 is positively correlated with -SH, a well-known antioxidant, and negatively correlated with LOOH, an oxidant. PON1 activity is significantly decreased after total thyroidectomy.