Five new humulane-type sesquiterpenes, mitissimols A (1), B (2), and C (3), and a mixture of mitissimol A oleate (4) and mitissimol A linoleate (5), were isolated from the fruiting bodies of Lactarius mitissimus. Their structures were elucidated on the basis of comprehensive spectroscopic techniques and necessary chemical methods. The relative stereochemistry of 1 was determined by single-crystal X-ray diffraction analysis.