Objective To investigate the small-world property of default mode network in relapsingremitting multiple sclerosis (RRMS) compared with the (matched) healthy control subjects,using a graph theory for resting-state functional network analysis.Methods Twenty four patients with RRMS and 24 age-,and sexmatched healthy controls were exanined with resting-state functional MRI (R-fMRI) and 3D-T1WI on Trio 3.0 Tesla.The R-fMRI data were preprocessed,then 20 regions of interest (ROIs) was defined and extracted from the default mode network.The functional connectivity between a pair of regions was defined as the Pearson's correlation coefficient in the time courses.Graph theoretical analysis was implemented and compared with the property of binary functional network.Further,the relationships were examined between the topological property of functional networks and the clinical parameters.Results In this study,functional network in the default mode network was conducted,and the small-world characteristics were observed in both RRMS and healthy control group.In the range of densities (Dmin:0.01∶0.48 ;Dmin =0.42),compared with healthy control group,RRMS groups had a slightly smaller normalized clustering coefficient (P＞0.05),a slightly larger normalized path length (P＞0.05),and a slightly decrease small-world index (P＞0.05).The left posterior cingulated cortex showed a significantly larger clustering coefficient in RRMS group (P=0.031) on the network threshold at Dmin.The area under a curve (AUC) for clustering coefficient measure curves of the left posterior cingulated cortex (density range of 0.42:0.01:0.48) between two groups were compared.The AUC result was similar to the Dmin result (P=0.031).Negative correlation was observed between the clustering coefficient of left posterior cingulated cortex and the Paced Auditory Serial Addition Test (PASAT) in both the Dmin(P=0.023) and the AUC (P=0.020).Conclusion The default mode network has small-world property in RRMS group.The significantly increased clustering coefficience is observed in the left posterior cingulated cortex,which may be a side effect.