The Orioles designated Atkins for assignment on Sunday, a move that coincided with the activation of right-hander Koji Uehara from the 15-day disabled list.
Atkins was batting .214 with one home run and nine RBI in 44 games. He scored only five runs, struck out 30 times in 140 at-bats and hit into seven double plays.
Signed to a $4.5 million, one-year contract in December, Atkins started at first base out of spring training. But as his struggles at the plate extended from weeks to months, he was replaced by the platoon of Ty Wigginton and Luke Scott.
Atkins started only five games this month, going 3 for 14 with one RBI.
"Unfortunately, things didn't work out for him here," interim manager Juan Samuel said. "It was getting kind of tough getting Atkins some at-bats. He got an opportunity early in the season. We just wish him luck."
Before signing with Baltimore, the 30-year-old Atkins had previously spent his entire career with Colorado, where he batted .289 with 98 homers in 773 games.
But Atkins lost his starting job last season, when he hit .226 with nine homers and 48 RBI after hitting .286 with 21 homers and 99 RBI in 2008.
His numbers with Baltimore weren't much better.
"We just couldn't get any power production from him, which limited his playing time," Samuel said.
Atkins packed his bags and left the clubhouse before reporters could talk to him. But Samuel said Atkins took the news without undue stress.
"He's a veteran. He understands," the manager said.
Although Atkins stumbled at the plate, he never groused in the clubhouse.
"He was very much a pro the whole time," Wigginton said. "He was always one of the first guys getting excited when somebody else got a big hit. He was a very good teammate."
Besides clearing space on the 25-man roster for Uehara, the Orioles made the move because outfielder Felix Pie (back) is expected to come off the disabled list by the end of the week.