The 38-year-old Rivaldo arrives on a loan from small Brazilian club Mogi Mirim, where he became the team's president after returning to Brazilian football last year.
He had been playing for Uzbekistan club Bunyodkor.
Financial details were not released, but Sao Paulo says it has the option of signing the 1999 world player of the year to a one-year contract extension.
Rivaldo was instrumental for the Brazil side that won the 2002 World Cup in South Korea and Japan.
He has also played for Deportivo La Coruna, AC Milan and Olympiakos, among others.