Ventrone, the six-year veteran has played for the Patriots and Browns and joins San Francisco by signing a one-year contract. Terms have not been disclosed.
Osgood has played in the league for seven years for the Chargers, Jaguars and Lions.
Osgood recovered a Kendall Hunter fumble on a kickoff in the first quarter of 2012's home-opening 27-19 win over Detroit.
The former San Diego State Aztec was named a first-team performer by Pro Football Writers in 2009 in his final season with the Chargers. He played in the Pro Bowl in 2006, 2007 and 2009.
Ventrone has played in 73 games since entering the league as an undrafted free agent in 2005 with the New England Patriots.
In order to make room for Ventrone, the 49ers waived fullback Jason Schepler. Wide receiver Joe Hastings was waived to accommodate Osgood.
The Villanova alum has been credited with 50 tackles and 39 special teams stops. He has spent the last four seasons with the Cleveland Browns.
The 49ers are hoping to improve their special teams coverage units after surrendering a kick-off return score to Jacoby Jones to open the second half of their 34-31 loss to the Ravens in the Super Bowl.