Background: Ayahuasca is a plant tea containing the psychedelic 5-HT 2A agonist N,Ndimethyltryptamine (DMT) and harmala monoamine-oxidase inhibitors. Acute administration leads to neurophysiological modifications in brain regions of the default mode network (DMN), purportedly through a glutamatergic mechanism. Post-acutely, ayahuasca potentiates mindfulness capacities in volunteers, and induces rapid and sustained antidepressant effects in treatment-resistant patients. However, the mechanisms underlying these fast and maintained effects are poorly understood. Here we investigated in an open-label uncontrolled study in sixteen healthy volunteers ayahuasca-induced post-acute neurometabolic and connectivity modifications, and their association with mindfulness measures. Methods: Using 1 H-magnetic resonance spectroscopy (MRS) and functional connectivity, we compared baseline and postacute neurometabolites and seed-to-voxel connectivity in the posterior (PCC) and anterior (ACC) cingulate cortex after a single ayahuasca dose. Results: MRS showed post-acute reductions in Glx (glutamate+glutamine), creatine and NAA-NAAG (N-acetylaspartate+Nacetylaspartylglutamate) in the PCC. Connectivity was increased between the PCC and the ACC, and between the ACC and limbic structures in the right medial temporal lobe (MTL). Glx reductions correlated with increases in the “Non-Judging” subscale of the Five Facets Mindfulness Questionnaire. Increased ACC-MTL connectivity correlated with increased scores on the Self-Compassion questionnaire. Post-acute neural changes predicted sustained elevations in “Non-Judging” two months later. Conclusions: These results support the involvement of glutamate neurotransmission in the effects of psychedelics in humans. They further suggest that neurometabolic changes in the PCC, a key region within the DMN, and increased connectivity between the ACC and MTL structures involved in emotion and memory, potentially underlie the post-acute psychological effects of ayahuasca. Key words: ayahuasca, psychedelic after-effects, magnetic resonance imaging, mindfulness, human