Provided is a nanoemulsion which has stability and to which preservative efficacy is imparted, in a bacterial contamination environment. This object is attained by a nanoemulsion which has an average particle diameter of 30 nm or less, has a particle size distribution index of 0.14 or less, does not contain particles of 100 nm or more, and contains, as a preservative, at least one selected from an organic acid (salt) and a biguanide-based compound.