Smolinski, 26, was batting .432 with two home runs and nine RBIs in 13 games for the Sounds after being claimed off waivers from the Rangers on June 21. He made his big league debut with Texas last year and hit .349 in 24 games, including .370 (10-for-27) with two home runs in seven games against the A's.
"It's a crazy game," said Smolinski, who hit just .133 in 35 games over three stints with the Rangers this year. "I have a lot of memories last year of playing against these guys, and now I'm excited to join them."
"He was swinging the bat really well in Nashville, and that's basically the same guy we saw last year at the end of the season," A's manager Bob Melvin said. "He killed us, so it's nice to have some additional power -- especially from the right side."
The A's have struggled to beat left-handers this year, going 5-16 when the opponent starts one, compared to 33-31 when facing a right-hander. The mark against southpaws is the poorest in the American League.
"We feel like we have a lineup that's better than the record would suggest," Melvin said, "but it's nice to add to it."
Smolinski will see time against left-handed starters in both left and right field.
"I'm excited about the club and about the opportunity I have, and I just want to make the most of it," he said.
• Left-hander Sean Doolittle played catch out to 60 feet Tuesday for the first time since hitting the disabled list with a strained left shoulder on May 28.
• Switch-pitcher Pat Venditte (right shoulder strain) remains on track to throw off the mound during the All-Star break. He's been playing catch out to more than 100 feet.
• Outfielder Coco Crisp is no longer dealing with kidney stones, Melvin said, but he's yet to resume baseball activity after getting an epidural in his strained neck.
Jane Lee is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.