To provide a moisture-proof coating method for a poly(lactic acid)-based resin which is excellent in barrier to steam, transparency and adhesiveness with a poly(lactic acid)-based resin.

In the moisture-proof coating method for a poly(lactic acid)-based resin, primer processing is preliminarily carried out with an aqueous dispersing element of a substituted or unsubstituted stylene or stylene derivative/,-unsaturated carboxylic acid copolymer, and then an aqueous dispersing element of an olefin/,-unsaturated carboxylic acid copolymer is applied. The dried coating film of the moisture-proof coating aqueous dispersing element for a poly(lactic acid)-based resin, which is gained by the above coating method, is excellent in barrier to steam, transparency and adhesiveness with a base material poly(lactic acid)-based resin.