Kasunic said Thursday the decision to retire wasn't easy, but it's time to spend more time with friends and family.
Kasunic was the senator when his district was the site of the Quecreek Mine rescue in 2002 and the crash of United Airlines Flight 93 on Sept. 11, 2001.
The 67-year-old Kasunic served six terms in the state House before getting elected to the Senate in 1994. Kasunic authored a major overhaul of Pennsylvania mine-safety laws, signed into law in 2008.
The 32nd District seat includes all of Fayette County and parts of Somerset, Washington and Westmoreland counties. The district's boundaries will shift slightly next year.