Hippocampus has always been suggested as the possible etiology for post-traumatic stress disorder (PTSD)[1]. However, until now most of the morphometric studies of hippocampus focus on whole volume and results remains inconsistent[2]. Given the fact that subfield of this structure bears distinctive histological characteristics and specialized functions, we aimed to investigate if PTSD is associated with structural alterations in specific subfield of hippocampal in a relatively large sample of adult patients with same stressor event. The study was approved by the local ethical committee. 67 DSM-IV criteria diagnosed PTSD patients after a severe earthquake and 78 age and sex matched non-PTSD adult survivors experience similar stressors were recruited and informed consents were obtained from all subjects. High resolution T1 weighted images were obtained using spoiled gradient recalled sequence (TR/TE = 8.5/3.4ms; flip angle = 12o; 156 axial slices with thickness = 1mm, field of view = 24×24cm2 and data matrix = 256×256) via a GE 3.0 T scanner. The structural data was automatically segmented using FreeSurfer software, volume of whole hippocampus and subfield including presubiculum, CA1, CA2-3, fimbria, subiculum, CA4-DG and fissure were extracted as well as intracranial volume (ICV). Statistical of volume differences between two groups were compared with SPSS using a general linear model (GLM) with age, years of education, duration from the events and ICV as covariates. Hemisphere, sex and diagnose were entered as fixed factors. Relationship between morphometric measurements with Clinician-Administered PTSD Scale (CAPS) score and illness duration were performed using Pearson’s correlation with SPSS.Demographic information for all subjects were shown in table1. Comparing to non-PTSD survivors, PTSD patients showed slightly enlarged hippocampal volumes in almost all subfield except left presubiculum and fimbria (both sides), though not reached statistical difference in current study. In male patients, there is significant correlation between CAPS score and volume of right CA2-3 (R2=0.197, p=0.034), right subiculum (R2=0.245, P=0.016) while duration was statistically correlated with right fissure (R2=0.247, P=0.016). In female patients, CAPS scores were significant correlated with volume of left presubiculum (R2=0.095, p=0.042), left subiculum (R2=0.09, p=0.048), and left CA4-DG (R2=0.099, p=0.037).The main finding of current study is the slightly enlargement of hippocampal in PTSD patients not long after the stressful event which differs from most previous study. We hypothesize this may demonstrate the responsive change of hippocampus after stress which cause cellular edema at an early stage of the disorder. The second find is the difference between genders referring to the role of hippocampus in PTSD etiology. Male patients seem to be more likely affected in right hippocampus, while in female patients left hippocampus seems contributed more. Further research to investigate relative functions shall be needed to clarify whether there are functional differences referring this particular structure.