Difference in human behavior is in part related to the prenatal brain exposure to androgen. Thus the brain functional network may vary with the magnitude of the androgen exposure, which can be estimated by the second to fourth digit ratio (2D:4D). Digit length was measured from the basal crease proximal to the palm to the tip of the digit on a photocopy of the right hand. We measured global functional connectivity of the gray matter in the human brain regions (“regional global connectivity,” rCG), and examined its correlation with 2D:4D. A 3 Tesla magnetic resonance imaging system (MRI, Philips) with a 32-channel head coil was used to obtain T1-weighted anatomical and resting state functional images of the healthy subjects (103 males and 96 females, mean (SD) age was 21±2 years old for both groups). During the acquisition (a series of three 5-min sessions), subjects were asked to stay awake with their eyes closed. Preprocessing of the blood oxygenation level dependent (BOLD) signal was performed using the analysis tools in SPM8 and in-house software developed on MATLAB, which includes head motion realignment, normalization with the standard template for echo planar imaging, and spatial/temporal smoothing and noise reduction. For each voxel (6x6x6 mm) in the gray matter, cross-correlation coefficients with all other gray matter voxels were calculated and averaged to determine each voxel’s rGC. The rGC values had significant relationship with 2D:4D at several regions as revealed by Pearsons’s correlation coefficient (t-test, p<0.05, corrected for multi-comparison with Monte Carlo simulation). We found marked sex difference in the hippocampus and adjacent regions (parahippocampus and fusiform gyrus): in male, negative correlation was seen in the bilateral regions, while positive correlation was seen in the left side in female. Further, in female, positive correlation was found at the left supra-parietal cortex, and negative correlation at the anterior and medial cingulate cortex and the superior medial frontal cortex. Hippocampus is known to be involved in various cognitive and emotional functions, as well as memory. Recent studies demonstrate that the hippocampal volume is affected by the prenatal androgen exposure as measured by the second to fourth digit ratio (2D:4D) in female. Thus, it is likely that the hippocampus may be a key region to construct sex-related identity. Our results suggest that, in female, the low hippocampal rGC is related to personality such as dominance and aggression (known to be related to low 2D:4D). In contrast, in male, the high hippocampal rGC may be related to the risk-taking decision making, since 2D:4D is known to be inversely related to the male day traders’ ability.