Sør-Audnedal (former name: Søndre Undal or Sør-Undal) is a former municipality in Vest-Agder county in Norway. It is located in the central part of the present-day municipality of Lindesnes.
The municipality of Sør-Audnedal means "southern Audnedal", since it is the southern part of the old Audnedal municipality which encompassed the Audnedalen valley. The name Audnedal (Old Norse: Auðnudalr) is named after the Audna river (Old Norse: Auðna) which runs through the valley ("-dalr") and empties into the Snigsfjorden. The river name means "destruction".
The municipality of Søndre Undal was established in 1845 when the old Undal municipality was divided into Nordre Undal and Søndre Undal. At that time, Søndre Undal had a population of 3,893. The name was later changed to Sør-Audnedal. On 1 January 1899, the western part of Sør-Audnedal, Spangereid, was separated to become a municipality of its own. The split left Sør-Audnedal with 2,958 inhabitants. On 1 January 1964, Sør-Audnedal was merged with Vigmostad and Spangereid to create the new municipality of Lindesnes. Prior to the merger, Sør-Audnedal had a population of 2,323.