It is known that L-menthol soothes smooth muscle motility. In order to use L-menthol in practice as a digestive tract motility soothing agent in digestive tract endoscopy, it is required to devise means of giving a preparation in which an L-menthol-containing solution remains stable and transparent or little cloudy over a long time after the production and which shows little foaming at the administration. To a smooth muscle motility soothing agent or a digestive tract motility soothing agent containing a relatively transparent L-menthol emulsion having an average particle size of less than 100 nm, a defoaming agent is further added. Thus, it is possible to obtain a preparation which remains stable over a long time, has a high light transmittance and suffers from no foaming in filling into a container or topical administration for, e.g., digestive tract endoscopy, thereby facilitating the observation of a disease area.
