To provide an external preparation for the skin, which is excellent in inhibitory effect against transdermal water evaporation triggered by a skin disease such as atopic dermatitis, psoriasis and eczema, prevents drying of the skin and is excellent in rough skin ameliorating effect.

The external preparation for the skin contains serine diamide of formula (1) (wherein R1 is an optionally hydroxylated 7-23C (un)saturated linear or branched alkyl group; and R2 is an optionally hydroxylated 2-18C (un)saturated linear or branched alkyl group).