Although the twin sisters land the cover for the 'Best Dressed' issue, nine other famous sisters are included on the list, from actresses Elle Fanning and Dakota Fanning, to songbirds Beyonce and Solange Knowles, and Britain's Kate Middleton and her sister Pippa Middleton.
Last month, the Duchess of Cambridge also landed on another most fashionable list, 'Britain's Best Dressed 2011' by Harper's Bazaar.
Vogue Fashion News Director and Editor Mark Holgate told Reuters: "It's been a year of sisters, most famously with Catherine and Pippa Middleton."
Holgate praised the Olsen sisters for wearing whatever they like.
"[The Olsens] get it right a lot of the time and then sometimes they don't get it right. That's actually great because it shows that it's their hands reaching into their wardrobes," Holgate said.
"They don't have someone telling them, 'This is cool, this is hot, this is what you should be wearing'. It comes from within them. It's instinctual.
"Look at what they've done with [their fashion labels] The Row and Elizabeth and James. They are legitimate fashion forces."
Earlier this year, Ashley expressed her interest in opening a fashion shop with her sister but said that it's "all a matter of timing".
Watch a video of Mary-Kate and Ashley Olsen for Stylemint below: