Decreased brain energy metabolism is correlated with cognitive impairment in Alzheimer's disease (AD). Accumulating evidence indicates that lactate and monocarboxylate transporters (MCTs) participate in brain energy metabolism. To date, changes in lactate level and expression of MCTs in AD remain unclear. This study was conducted to detect the changes in lactate content and expression of MCT2 in Aβ25-35-treated rat model of AD. Sprague-Dawley rats were randomly divided into control and model groups, which received bilateral intrahippocampal injections of saline and Aβ25-35, respectively. Cognitive functions were detected by Morris water-maze test. Lactate content in the cerebral cortex and hippocampus was measured by absorbance assay. The MCT2 level in the brain was examined by immunohistochemistry and Western blot. Morris water-maze test showed that the model group exhibited impaired learning and memory compared with the control group. Lactate content in the cerebral cortex and hippocampus was decreased in the model group compared with that in the control group. Immunohistochemistry and Western blot showed that the expression of MCT2 in the model group significantly decreased compared with that in the control group. Results indicate that decreased lactate content and downregulated MCT2 expression in the cerebral cortex and hippocampus reflected impaired energy metabolism in the brain, which may participate in the pathologic progression of AD.