Middleton, in fourth place, is a newcomer on the annual list of Glamour magazine and ranks higher than her sister Pippa Middleton, who is 47th.
"Harry Potter" star Emma Watson slipped from the top spot in 2011 to second place in the top 50 list.
Former X Factor judge Cheryl Cole also dropped from second to eighth in the rankings, but the magazine says the pop star has the "fashion factor nailed".
Spice Girl turned fashion designer Victoria has shot up 12 places to third, with the magazine praising the "adorable co-ordinating looks" she shares with "her new favourite accessory" - baby daughter Harper Seven.
