The purpose of the present invention is to provide technology for stably emulsifying a liquid composition containing a terpenoid while said liquid composition is in a transparent state. Provided is an O/W microemulsion that comprises (A) an essential oil containing a terpenoid, (B) ethanol, (C) a polyglycerin fatty acid ester, and (D) a polyoxyethylene sorbitan fatty acid ester, and in which (A):(B) = 1:2.5-40 in terms of mass.COMPOSICIÓN DE MICROEMULSIÓN DE ACEITE EN AGUA (O/W) QUE COMPRENDE UN ACEITE ESENCIAL QUE CONTIENE UN TERPENO, ETANOL, UN ÉSTER DE ÁCIDO GRASO DE POLIGLICEROL, Y UN ÉSTER DE ÁCIDO GRASO DE POLIOXIETILEN SORBITÁN; Y PRODUCTO QUE COMPRENDE DICHA COMPOSICIÓN.