Mary Lou Rath (née Schmitt) (born June 17, 1934) is an American politician who served as a member of New York State Senate from 1993 to 2008.
Rath was born in Kenmore, New York to Aloysius Casper "Lloyd" Schmitt and Margaret M. Cassidy.
Her parents divorced and Rath's mother remarried to George Louis Whetzle.
In January 2007, she was appointed to the post of deputy majority leader for state/federal relations, making her the only woman in the Senate Republican leadership.
She announced her retirement in 2008 and was succeeded by Erie County Legislator Michael Ranzenhofer.