Puberty is a sensitive period of brain development with the structural reorganization and pruning of neuronal circuits. During puberty, the hypothalamus–pituitary–gonadal (HPG) axis is activated, leading to a series of pubertal hormone level changes. These pubertal hormones are thought to play an additional role in regulating gray matter development during puberty¹. But the relationship between them remains debated and little is known how different brain regions may be altered directly related to gonadotropins level over the earliest stage of puberty. We therefore investigated the impact of the HPG-axis activity on brain morphometry and then try to find out the potential effects of pubertal hormones on these anatomical changes.The study was approved by the local research ethics committee, and written informed consent was obtained from parents or guardians. Pubertal hormone levels were obtained through GnRH stimulation test. A total number of 52 subjects including 34 HPG-axis activated girls and 18 inactivated girls matched with age were recruited and scanned structural MRI. All the subjects are right-handed. The MRI examinations were performed on a 3T GE HDxt scanner (General Electric, Milwaukee) with an eight-channel phase array head coil. High-resolution T1-weighted images were acquired with a volumetric 3D-FSPGR sequence (TR=8.89ms, TE= 4.02ms, flip angle= 15°, field of view=256×256, slice thickness=1 mm, 160 slices). Cortical modeling and volumetric segmentation of structural MRI data were performed with the FreeSurfer package (version 5.1.0, http://surfer.nmr.mgh.harvard.edu/)²; While voxel-based analysis was performed using the VBM8 toolbox (http://dbm.neuro.uni-jena.de/vbm) to fully detect the potential structural changes in these subjects³. Group comparisons were achieved using a general linear model with age, BMI, and total intracranial volume included as covariates. Subsequently, Pearson's correlation was used to explore the relationship between structural changes and puberty hormone. The ability of pubertal hormones to predict the cortical thickness and gray matter volume independent of age was investigated using multiple linear regression analysis. One outlier for the LH concentration in this sample was checked and ruled out in the correlation and regression analysis. Demographics like age and BMI were not significantly different between the two groups (p>0.05). HPG-axis activated girls had less cortical thickness in the left inferiorparietal relative to comparison subjects (corrected after Monte Carlo simulation p<0.05). Cortical thickness and hormone levels were not significantly correlated, but it suggested a trend for a positive association with LH level (P=.060). Meanwhile, gray matter volume was greater in the left precuneus in the focused group, relative to the control group (corrected after FWE, p<0.05). We found a positive correlation between circulating FSH and volume of the left precuneus (P= 0.046) after excluded one outlier. Multiple linear regression analysis, with circulating FSH level, LH concentration and age as predictors, found that increased circulating FSH level significantly predicted the increase of gray matter volume in this region. By studying these girls in the pre or earliest stage of puberty with an accurate hormone test and objective MRI measuring, the current study adds important new evidence about gray matter changes brought by the HPG-axis activated after controlling for age. The relation of LH to cortical thickness indicated a tendency that faster LH-related cortical thinning in the left inferiorparietal in activated girls than in comparison subjects, future study with larger sample size might help to verify their association. The relationship between FSH and gray matter volume of precuneus indicated faster FSH-related gray matter volume increase in this region⁴.This study demonstrates that there is some puberty-related maturation of the brain morphometry that is not confounded by age in the earlier stage of puberty, which might be directly or indirectly mediated by hormone production.