Zambrano's agent Peter Greenberg says Elizabeth Mendez Zambrano was abducted Sunday morning from her son's farm near Maracay in central Venezuela.
In Venezuela, which is home to dozens of major leaguers, the families of wealthy athletes are periodically targeted by kidnappers. Rockies catcher Yorvit Torrealba's son and brother-in-law were released by kidnappers a day after they were abducted in June.
Zambrano played seven big league seasons for Tampa Bay, the New York Mets, Toronto and Baltimore. The right-hander has a career record of 45-44 with a 4.64 ERA.
He hasn't appeared in a major league game since 2007.