Previous neuroimaging studies suggest that dysfunction of cortico-striato-thalamo-cortical(CSTC)circuits is associated with the pathogenesis of obsessive-compulsive disorder(OCD),but the results show inconsistency.In the present study,magnetic resonance spectroscopy(MRS)which is a non-invasive in vivo method was applied to explore the brain metabolism of psychotropic-naive adult patients with OCD,focusing on anterior cingulate cortex(ACC)and bilateral thalamus areas.To investigate the neurobiological alterations of OCD,we used LCModel to quantify metabolites measured by MRS and multivariate statistics methods,specifically partial least squares discriminant analysis(PLS-DA)to identify biomarkers which are vital to neuropathology of obsessive-compulsive disorder,and these two statistic methods obtained similar results in right thalamus.The results showed that patients with OCD had abnormal glutamatergic signals in acc-thalamus circuit,such as Glu/Cr in both anterior cingulate cortex and right thalamus,also reduced Glx levels in right thalamus.In addition,increased choline compounds were discovered in the bilateral thalamus of patients,such as significant higher GPC and Cho levels in right thalamus of patients,and significant higher GPC/Cr and Cho/Cr levels in left thalamus of patients were observed.Meanwhile,through partial least squares(PLS)and Pearsons correlation we found that therere strong relationship between the level of metabolites and clinical scores of patients,especially the role of glutamatergic signals in compulsive behaviours.The findings might prove the hypothesis about the abnormalities of glutamatergic and cholinergic signals in anterior cingulate cortex and thalamus areas of patients with OCD,which would make it possible to provide effective basis for its early diagnosis and the evaluation of treatment.