Background/Aim: Puberty is a mysterious process and much is yet to be revealed. Recently, it has been reported that MKRN3 gene may be a cause of familial precocious puberty. In healthy children, serum MKRN3 decreased at the onset of puberty and was negatively correlated with gonadotropins. The aim of this study was to evaluate the serum level of MKRN3 concentration in precocious puberty patients and examine the changes of MKRN3 in GnRHa treatment. We also investigated the usefulness of serum MKRN3 as screening for precocious puberty. Methods: In total, 41 girls with CPP and 35 prepubertal girls were enrolled. Baseline serum MKRN3 levels were measured and compared in patients and normal controls. Patients with CPP were measured serum MKRN3 and gonadotropin levels every 6 months for one year while receiving GnRH agonist treatment. Receiver operating characteristic (ROC) curves were used to evaluate the diagnostic value of serum MKRN3. Results: Serum MKRN3 levels were much lower in the patient group than in the normal group, 521.00 ± 608.50 and 1282.24 ± 791.26 (pg/ml), respectively (p=0.005). Gonadotropin levels were significantly decreased during GnRHa treatment in patients. There was no significant change in MKRN3 levels during GnRHa treatment in patients. The area under the ROC curve of serum MKRN3 for predicting precocious puberty was 0.758 (optimal cut - off value, 932.91 pg/ml), with a sensitivity of 83.9% and a specificity of 88.8%. Conclusions: These findings indicate that serum MKRN3 is significantly reduced in patients with precocious puberty and is not affected by GnRH agonist treatment. Serum MKRN3 may be a useful biomarker as a screening tool to diagnose precocious puberty.