Frau came through Sochaux's youth ranks and scored 59 goals in 174 league appearances during his first spell, but left in 2004 to join former league champions Lyon.
After playing for Paris Saint-Germain, Lille and Caen the 33-year-old found himself at Al-Wakrah in Qatar, where he scored five goals in 20 appearances.
His contract was not renewed at the club, enabling him to sign for Herve Renard's side on a free transfer.
"Pierre-Alain Frau signed this Monday, November 25 a contract with FCSM until the end of the 2013/2014 season," a statement on the club's website confirmed.
"He convinced the coaching staff and club officials that he could strengthen the playing staff for this season in Ligue 1 and bring his experience and qualities."
Sochaux are bottom of the table with eight points from 14 matches and have only scored 12 goals so far this season.
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