The pair, who co-run clothes ranges The Row and Elizabeth and James, said that they aim to have a store for themselves.
Ashley told The Modestry: "I think every designer would say they'd love to open their own store, just because when you produce a collection, this whole room will be filled with God only knows how many racks and 150 pieces.
"What hits the stores is maybe ten pieces, in different colourway. So it would be nice to be able to represent it in your own way.
"But it's all a matter of timing and when it makes sense, and it's a really big undertaking, so it depends."
Ashley also admitted that she and her sibling often wear unusual clothes to prevent their pictures being taken.
She added: "That moment for us was us waking up, going to school, and not wanting anyone to take our picture. Kind of a piece of protection."
The sisters were inducted into the Council Of Fashion Designers Of America in 2009.
Mary-Kate and Ashley recently insisted that they take fashion seriously.