Kentucky Derby winner Mine That Bird was second and Musket Man third.
Jockey Calvin Borel, who was aboard Mine The Bird in the Kentucky Derby, was the first jockey to win the Kentucky Derby winner and then ride a different horse in the second leg of racing's Triple Crown.
Rachel Alexandra is the first filly in the Preakness since 1999 and the first to win the Preakness since Nellie Morse in 1924. Rachel Alexandra was the 9-5 post-time favorite and started from the far outside post.
The filly hit the top of the stretch with a clear lead but Mine That Bird was charging from the back of the field. Mine That Bird passed Musket Man who was third in the Kentucky Derby but ran out of room as Rachel Alexandra won by one length in front.
The time for the 134th Preakness Stakes on a fast track was 1:55.08 for the 1 3/16 miles.
Rachel Alexandra is perfect in her five starts this year. She added $710,000 to her earnings. She has won eight of 11 lifetime starts for $1,668,354.