The pair are gold medal favorites for the Beijing swim competition starting Aug. 9 after 22-year-old Sullivan set the 50-meter freestyle world record, and 20-year-old Rice set world records in the 200- and 400-meter individual medley events, at the Australian championships in March.
Sullivan on Wednesday said he and Rice were "focusing purely" on Beijing this month, adding both were "a bit selfish in that we want to swim to the best of our ability."
"We both mutually agreed that being together is something that probably won't work during this month, and decided to have a break," he said in Kuala Lumpur where he and Rice are training with the Australian swim team ahead of Beijing.
Rice did not speak to the media.
Sullivan said the split happened a few weeks ago, and they let their friends know about it by changing the status on their online Facebook pages to "no longer in a relationship."
"We are still great friends and probably have spoken more and seen each other more than (when) we were together. Things are not much different." he said, adding that the split was not a distraction for him.
He did not rule out renewing his romantic relationship with Rice after the games.
"You never know what the future holds but we are not thinking about that at the moment," Sullivan said. "We are just looking at the month ahead and making sure we do 100 percent in our own preparations and focus 100 percent on ourselves.
"We have made this decision with our best interests at heart, and yeah it is working well so far."
Australian swim team coach Alan Thompson said what Sullivan and Rice do is their business.
"Certainly it doesn't concern anyone else in the team, and it's not a nasty breakup. It's not my business unless it does disrupt the team and it certainly hasn't done that," he said. "I respect their decision."
At the Australian championships in March, Sullivan clocked 21.28 seconds in the 50 meters, after lowering the mark to 21.41 in the semifinals, which also broke the world record of 21.50 set by France's Alain Bernard at the European championships in Eindhoven, Netherlands a week earlier.
Rice's first world record was in the 400 individual medley, finishing in a time of 4:31.46 to improve on American Katie Hoff's mark of 4:32.89 set at the world championships in Melbourne last year. Her second record came in the 200 IM at 2:08.92, breaking the previous record of 2:09.72 by China's Wu Yanyan set in 1997.
Rice is based in Brisbane on the east coast and Sullivan lives in Perth on the west coast, more than four hours by plane. The couple met just before the 2006 Commonwealth Games.
After their world record feats, Rice had spoken of the difficulties in maintaining a long distance relationship.
"It's always been really hard," she said at the time. "Talking on the phone, you can interpret things the wrong way and that's really hard."
Laurie Lawrence, the official motivator for Australia's Olympic team, said both swimmers are too professional to let the split affect them.
"They've been training for this moment for so long they'll have their mind right on the job. They won't be distracted by anything," he told Australia's Nine Network television.
