The assault happened at about 2:40 a.m. Friday at the Saxon Suites student housing complex in the 300 block of De Neve Drive, according to the UCLA Police Department.
"The suspect entered victim's bedroom while she was in bed. The suspect sexually assaulted her and then left the room in an unknown direction," police said in a news release.
Police described the suspect as a white man in his 30s, heavy set with a curly beard. He was wearing all black clothing and a beanie, police said.
The victim was medically treated at the scene.
"There's like windows on the side of each apartment, and I heard that he came in through the window which is the easiest way to get in," UCLA student Kyla Nassir said.
Although UCLA is on summer break, some students are attending summer school and others are attending summer programs.
Anyone with information on the case is asked to call UCLA police at 310-825-1491.