The double helix structure of DNA was first discovered in 1953 by Crick and Watson at the University of Cambridge. It appeared in April 1953 in the scientific paper where James Watson and Francis Crick presented the structure of the DNA helix, the molecule that carries genetic information from one generation to the other.

Nine years later, in 1962, they shared the Nobel Prize in Physiology (Medicine) with Maurice Wilkins, for solving one of the most important of all biological riddles about man and the structure of DNA. The modern era of biology began as human understanding of the double helix structure of DNA occurred.

This discovery by Crick and Watson has been described by some other biologists and Nobel laureates as the most important scientific discovery of the 20th century.

More Info: en.wikipedia.org