This case-control study aims to evaluate the oxidant-antioxidant balance in girls having central precocious puberty (CPP) and premature thelarche (PT). Thirty-four girls having CPP, 24 girls having PT, and 49 healthy growing girls between 7 and 9 years of age admitted to child health supervision were enrolled. Total antioxidant and oxidant capacity, myeloperoxidase, catalase, superoxide dismutase, total thiol, native thiol, and disulfide levels were analyzed in serum samples. Low total oxidant status (<12.0) was found to be highest in the CPP group, lowest in the control group, and the PT group was in between them. After controlling bone age and z score for body mass index, generalized linear models revealed lower oxidative stress index values in the CPP and the PT groups than the control group. Other studied parameters did not differ among groups. Precocious puberty in girls is associated with some changes in the oxidant-antioxidant status.