Objective To study the clinical value of basal serum gonadotropin levels in the diagnosis of precocious puberty in girls and determine the optimal cut-off points values. Methods A total of 101 girls with central precocious puberty (CPP) and premature thelarche( PT) were enrolled from Developmental Pediatrics of Shengjing Hospital from January 2012 to July 2013.luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured by chemiluminescent immunometric assay.The receiver operating characteristic (ROC) curve was used to analyze the area under the ROC curve (AUC) for basal serum LH, FSH, LH/FSH ratio, the cut-off points, the sensitivity and specificity. Results The AUC of LH, FSH, LH/FSH ratios among 101 girls were 0.834, 0.742 and 0.808 respectively.The AUC of 83 girls after excluding the girls less than 4 years were 0.898, 0.842 and 0.854.Without the girls below 6 years, the AUC of 60 girls were 0.895, 0.845 and 0.870, respectively.When LH cut-off points were 0.36 U/L, 0.36 U/L, 0.38 U/L in each group, the sensitivity were 77.6% , 78.7%, 75.0%, and the specificity were 81.8%, 97.2%, 100% respectively.When FSH cut-off points were 2.51 U/L, 3.63 U/L, 3.48 U/L, the sensitivity were 85.7%, 68.1%, 69.4%, and the specificity were 57.7%, 91.7%, 91.7% respectively.When LH/FSH ratio cut-off points were 0.09, 0.03, 0.03, the sensitivity were 77.6%, 85.1%, 83.3%, and the specificity were 75.0%, 77.8%, 83.3% respectively. Conclusions Basal serum LH has a higher specificity for diagnosis of CPP.In addition, the specificity can be elevated gradually when excluding the girls below 4 years and 6 years.When the basal serum LH level is higher than 0.36 U/L, the diagnosis of CPP can be confirmed among the girls over the age of 4 years in combination with clinical manifestation.However, when the basal serum LH is lower than 0.36 U/L, we cannot refute the presence of CPP in girls of any age.