Mortdale is a suburb in southern Sydney, in the state of New South Wales, Australia. Mortdale is located 20 kilometres south of the Sydney central business district and is part of the St George area. Mortdale lies across the local government areas of the City of Hurstville and Municipality of Kogarah. Mortdale extends south to Lime Kiln Bay, on theGeorges River. Mortdale Heights is a locality in the south-western corner of the suburb, in which all but one street names start with "B".