The fashion houses behind brands including Christian Dior and Gucci have said they will stop using underweight models for their catwalk shows.
The move was made amid criticism that the industry encourages eating disorders.
Models must be bigger than a French size 32, which typically equates to a UK size six or US size zero.
The firms will also not use models under the age of 16 for adult clothes.
The move by the two French firms comes after a law banning ultra-thin models came into effect in the country in May.
Those who break the French law face fines of up to €75,000 or jail sentences of up to six months.
Models must also be able to present a valid medical certificate that they are fit to work.