Sen. Jon Kyl, R-Ariz., said Thursday he won't run for re-election next year, becoming the fifth senator to decide not to seek another term.
Kyl, the second-ranking Senate Republican leader, said at a news conference in Phoenix there was "nothing negative" prompting his decision to retire at the end of his third six-year term.
"It's time for me to have an opportunity to do something else" and give others a chance to serve in the Senate, Kyl said.
"My heart says it's time."
As Senate minority whip, Kyl, 68, is the chief vote-counter for Republicans, a post he was slated to give up next year. He served four terms in the House before his 1994 election to the Senate, where he has been a key architect of the Republican agenda in recent years, including the push for tax cuts.
As a member of the Judiciary Committee, he played a major role in opposing President Barack Obama's Supreme Court nominations of Sonia Sotomayor and Elena Kagan, both of whom won Senate confirmation.
Other senators who have decided not to run next year are Kay Bailey Hutchison, R-Texas; Democrats Kent Conrad of North Dakota and Jim Webb of Virginia and Democrat-turned-independent Joe Lieberman of Connecticut.
Meanwhile, retiring Rep. Jane Harman, D-Calif., said she will resign her House seat on Tuesday to allow for a special election in early June to replace her.