Terpinolene is a cyclic monoterpene compound found in some Labiatae herbs. In our previous study, we evaluated the sedative effect of inhaled essential oils of Microtoena patchoulii leaves in mice and isolated terpinolene as an active ingredient. We investigated the structure–activity relationships of terpinolene to identify the structural part essential to its sedative effect. Comparison of terpinolene analog activities showed that a double bond in the side-chain or pi bonds in the six-membered ring play important roles in the sedative effect. In another experiment using olfactory impaired mice, we further revealed that inhaled terpinolene exerted the effect after nasal absorption into the body.