| Honorific-Prefix: | The Honourable |
| Rose-Marie Losier-Cool | |
| Office1: | Speaker Pro Tempore of the Senate of Canada |
| 1Namedata1: | Gildas Molgat Dan Hays |
| Term Start1: | November 17, 1999 |
| Term End1: | October 7, 2002 |
| Predecessor1: | Gerry Ottenheimer |
| Successor1: | Lucie Pépin |
| Office2: | Government Whip in the Senate |
| Primeminister2: | Jean Chrétien |
| Leader2: | Jack Austin |
| Term Start2: | January 15, 2004 |
| Term End2: | February 5, 2006 |
| Predecessor2: | Bill Rompkey |
| Successor2: | Terry Stratton |
| Office5: | Canadian Senator from Tracadie |
| Term Start5: | March 21, 1995 |
| Term End5: | June 18, 2012 |
| Nominator5: | Jean Chrétien |
| Appointer5: | Roméo LeBlanc |
| Predecessor5: | Roméo LeBlanc |
| Successor5: | Paul McIntyre |
| Birth Date: | 18 June 1937 |
| Birth Place: | Tracadie, New Brunswick, Canada |
| Party: | Liberal |
Rose-Marie Losier-Cool (born June 18, 1937) is a retired Canadian Senator for New Brunswick.
A member of New Brunswick's Acadian community, Losier-Cool worked as a teacher for thirty-three years, two decades of which were spent at École secondaire Népisiguit in Bathurst, New Brunswick.
She was elected the first woman president of the Association des enseignantes et des enseignants francophones du Nouveau-Brunswick in 1983 and has sat on the board of directors of the Canadian Teachers' Federation. She was awarded the Teacher of the Year Award for non-sexist teaching by the government of New Brunswick in 1993. In 1994–95, she was Vice-President of the New Brunswick Advisory Council on the Status of Women.
Losier-Cool was appointed to the Senate on March 21, 1995 on the advice of then Prime Minister of Canada Jean Chrétien and sits as a Liberal. In January 2004, she was appointed Government Whip in the Senate, the first woman ever to hold this role. Loisier-Cool left the Senate upon reaching the mandatory retirement age of 75 on June 18, 2012.