The symbolic clock is maintained by the Bulletin of the Atomic Scientists and represents their assessment of the danger of a global nuclear holocaust.
They moved the clock from six to five minutes to midnight, citing nuclear proliferation, the Japanese nuke meltdown and the threat of terrorists acquiring a dirty bomb.
It was previously set at five minutes to midnight from 2007-2010.
"Two years ago, it appeared that world leaders might address the truly global threats that we face. In many cases, that trend has not continued or been reversed. For that reason, the Bulletin of the Atomic Scientists is moving the clock hand one minute closer to midnight, back to its time in 2007," scientists said in a statement.
The clock was closest to midnight - two minutes - in 1953 after the U.S. successfully tested a hydrogen bomb.
The Associated Press contributed to this report.