Although manganese (Mn) is an essential metal ion biological cofactor, high concentrations could potentially induce an accumulation in the brain and lead to manganism. However, there is no "gold standard" for manganism assessment due to a lack of objective biomarkers. We hypothesized that Mn-induced alterations are associated with metabolic responses to manganism. Here we use an untargeted metabolomics approach by performing ultra-high performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF/MS) on control and Mn-treated rat plasma, to identify metabolic disruptions under high Mn exposure conditions. Sprague-Dawley rats had access to deionized drinking water that was either Mn-free or contained 200 mg Mn per L for 5 weeks. Mn-exposure significantly increased liver Mn concentration in comparison with the control, and also resulted in extensive necrosis and dissolved nuclei, which suggested liver damage from hepatic histopathology. Principal component analysis readily distinguished the metabolomes between the control group and the Mn-treated group. Using multivariate and univariate analysis, Mn significantly altered the concentrations of 36 metabolites (12 metabolites showed a remarkable increase in number and 24 metabolites reduced significantly in concentration) in the plasma of the Mn-treated group. Major alterations were observed for purine metabolism, amino acid metabolism and fatty acid metabolism. These data provide metabolic evidence and putative biomarkers for the Mn-induced alterations in plasma metabolism. The targets of these metabolites have the potential to improve our understanding of cell-level Mn trafficking and homeostatic mechanisms.