Sør-Aurdal is a municipality in Oppland county, Norway. It is part of the traditional region of Valdres. The administrative centre of the municipality is the village of Bagn.The parish of Søndre Aurdal was established as a municipality on 1 January 1838 (see formannskapsdistrikt). The area of Bruflat was transferred from Sør-Aurdal to Etnedal on 1 January 1894.
The Old Norse form of the name was Aurardalr. The first element is the genitive case of the old river name Aur (now called Bøaelva) and the last element is dalr which means "valley" or "dale". The old river name is derived from aurr meaning "gravel". The name Sør-Aurdal means '(the) southern (part of) Aurdal'. (The parish of Aurdal was divided in 1805.)