Objective To investigate the characteristics of gray matter volume in Obsessive Compulsive Disorder (OCD) patients compared with healthy controls, and to explore the correlation between brain regions with altered gray matter volume and the patients'cognitive function and clinical symptoms. Method Thirty-six patients with first-episode OCD and 35 healthy controls who were matched by age, gender and education level were selected and examined by MATRICS Consensus Cognitive Battery (MCCB) and Yale-Brown Obsessive Compulsive Scale (Y-BOCS). The head MRI and the Voxel-based morphometry was used to test the volume of gray matter. The correlation analysis was conducted to analyze the correlation between brain areas with altered gray matter volume and patients'cognitive function and Y-BOCS results. Results Compared with the control group, the OCD group had increased gray matter volume in frontal parietal lobe (postcentral gyrus-L, precentral gyrus-L) (t=4.299, P<0.0005, voxels>100) and temporal-limbic system (fusiform gyrus-L, superior temporal gyrus-L, medial temporal lobe-L, parahippocampal gyrus-L) (t=4.841, P<0.0005, voxels> 100). Meanwhile, the volume of gray matter decreased in bilateral anterior cingulate gyrus (t=-4.181, P<0.0005, voxels>100). In the case group, there were a positive correlation between the volume of gray matter in the temporal lobo-limbic system and social cognition score (r=0.347,P=0.038) and a positive correlation between the volume of gray matter in the anterior cingulate gyrus and obsessions score (r=0.416,P=0.012). Conclusion Patients with OCD have abnormal gray matter volume in a wide range of brain regions, including the frontal parietal lobe, the temporal-limbic system, and bilateral anterior cingulate gyrus, among which the volume of gray matter in the temporal-limbic system is correlated with social cognition, and gray matter volume in the anterior cingulate gyrus is correlated with obsessions.