Zaun gets a $500,000 signing bonus and a $1.4 million salary next season. His deal includes a $2.25 million club option for 2011 with a $250,000 buyout.
The 38-year-old split last season with Baltimore and Tampa Bay, hitting a combined .260 with eight home runs and 27 RBIs in 90 games. He made a total of 74 starts behind the plate, including 49 games with the Orioles and 25 games with the Rays.
Zaun has a career batting average of .251 with 86 homers and 432 RBIs during 15 seasons with Baltimore, Florida, Texas, Kansas City, Houston, Colorado, Toronto and Tampa Bay.
Milwaukee agreed to a minor league contract with outfielder Trent Oeltjen, who was invited to major league camp.