PURPOSE: To obtain an external preparation having skin color-lightening and stains and freckles-preventing effects with high safety without side-effects such as skin roughening and rashes by using an unsaturated straight-chain fatty acid or its derivative as an active ingredient.

CONSTITUTION: The subject preparation is obtained by using an unsaturated straight-chain fatty acid of 4 to 17 carbon atoms having 1 to 4 unsaturated bonds distributing in arbitrary positions other than the chain terminal opposing to the carboxyl group on the alkyl chain or its derivative, as an active ingredient in combination with conventional base materials and auxiliary agents in a usual manner to give the subject preparation. At this time, the addition of an ultraviolet absorber and an antioxidant is preferred. The amount of the unsaturated fatty acid used is 0.001 to 5wt.% in cosmetics and 0.001 to 10wt.% in medicines. 10-Petandecenoic acid and 9-hexadecenoic acid are excluded from the unsaturated straight-chain fatty acid as an active ingredient.