We discovered a new species of Ectomycorrhizal Lactarius belonging to the Russulaceae family: Lactarius crocogalum. The fruit body and root-tip specimens were collected in the tropical peat swamp forest of Sebangau National Park (Central Kalimantan, Indonesia). The fruit bodies were assessed by microscopic and macroscopic morphology features, as well as molecular screening of two nuclear genes, ITS and LSU, whereas the DNA extracted from the root tips was used to validate the ectomycorrhizal ecology of the fungus and to identify the tree host. The obtained ITS and LSU sequences were blasted against a customized database of available sequences of closely related Lactarius strains. The results validate both the taxonomy novelty and the ecological role of Lactarius crocogalum as ectomycorrhizal symbiont of a fagaceous tree.