The 39 year-old Australian, who is wanted by Interpol over a charge of rape and sexual assault in Sweden, said there were some references to extraterrestrial life in yet-to-be-published confidential files obtained from the American government.
He did not revealed what information was contained in the diplomatic memos obtained by the website.
It also remains unclear when they will be published.
Assange said his website, under considerable strain in recent days over its "Cablegate" series of leaks, received emails from "weirdos" claiming to have seen UFOs.
"Many weirdos email us about UFOs or how they discovered that they were the anti-christ whilst talking with their ex-wife at a garden party over a pot-plant," the Telegraph quoted him as saying, when asked if any of the documents he had received referred to extraterrestrial life.
"However, as yet they have not satisfied two of our publishing rules. 1) that the documents not be self-authored; 2) that they be original.
"It is worth noting that in yet-to-be-published parts of the cablegate archive there are indeed references to UFOs," he added.
Assange's comments were made during a webchat with The Guardian.