Tsao, 34, has a 4.40 ERA in 25 games between Double-A Tulsa and Triple-A Oklahoma City this season with 39 strikeouts and nine walks in 30⅔ innings, including 31 strikeouts and five walks in 21 games in OKC, with five saves in his first professional season in the United States since 2008.
Tsao has gone his last 10 appearances without issuing a walk, and has 10 strikeouts since his last walk, on June 5.
The Dodgers signed Tsao to a minor league deal on January 3, a move that had to be cleared by Major League Baseball because the Taiwanese right-hander was serving a lifetime ban from the Chinese Professional Baseball League for involvement in a game-fixing scandal in 2009.
Tsao pitched in six games during spring training and impressed his teammates.
"He gives me a lot of options to play with, whether it's backdoor breaking balls, cutters inside, fastballs up," said catcher Yasmani Grandal in March. "He can bring it too. I didn't know he could bring it that hard."
Tsao last pitched in the major leagues in 2007 with the Dodgers, putting up a 4.38 ERA in 21 relief appearances, with 16 strikeouts and eight walks in 24⅔ innings.
The Dodgers on Tuesday had Juan Nicasio and Ian Thomas each throw two innings of relief, throwing 46 and 30 pitches, respectively. This was one day after six relievers combined with Eric Surkamp for a bullpen game, including Yimi Garcia throwing 43 pitches in two innings and Pedro Baez throwing 28 pitches in his one inning, his third appearance in four days.
Manager Don Mattingly said after Tuesday's game that using Nicasio and Thomas, the latter called up on Tuesday for Surkamp, helped give certain pitchers a needed day off, but that the bullpen wasn't quite out of the woods yet.
"We'll see," Mattingly said. "We’re still talking about some things with that and what we’ll do with it."
Tsao last pitched on Saturday, throwing 37 pitches in two innings.
The Dodgers will have to make a corresponding transaction to make room for Tsao on the 40-man roster.