This study characterized the acaricidal activity of constituents of patchouli oil extracted from (Pogostemon cablin (Blanco) BENTH) against the house dust mite, Dermatophagoides farinae. A new compound, 2-(1,3-dihydroxy-but- 2-enylidene)-6-methyl-3-oxo-heptanoic acid (DHEMH), was isolated from patchouli oil and characterized by 1H-NMR, 13C-NMR, LC-MS and elemental analysis (EA). This active component was identified as the hydrolysate of pogostone. Fifteen other constituents found in patchouli oil were also identified by GC-MS, including patchouli alcohol and pogostone. LD 50 studies carried out over 24 h using contact toxicity tests identified DHEMH as the most toxic compound to D. farinae (2.04 μg/cm2), followed by patchouli oil (6.11 μg/cm 2), benzyl benzoate (BP) (9.31 μg/cm 2) and dibutyl phthalate (DBP) (58.52 μg/cm 2). In vapor phase toxicity tests, all of these compounds were more effective in closed than open containers, indicating that the most efficient mode of delivery for these compounds is the vapor phase. These results indicate that DHEMH and patchouli oil merit further study as potential agents for the control of D. farinae. © 2012 The Pharmaceutical Society of Japan.