Yale University unveiled its biggest expansion in nearly four decades on Saturday, with plans to build two new residential colleges that would raise undergraduate enrolment by 15 percent.

The new colleges at the Ivy League school in New Haven, Connecticut, would open in 2013 and increase enrollment to about 6,000 students, President Richard Levin said in a letter to alumni posted on Yale's website.

The last significant increase in the student body came with the admission of women in 1969, he said. Undergraduate enrollment has fluctuated between 5,150 and 5,350 in recent years.