Mersey St Mary's was an electoral ward of Trafford covering the eastern part of Ashton upon Mersey in Sale, Greater Manchester.
The ward was abolished in 2004, and its area split between the new Ashton upon Mersey and St Mary's wards. For the ward's entire existence, it elected Conservative councillors on all but one occasion â at its creation in 1973, it elected 1 Liberal councillor alongside 2 Conservative councillors.