Saint-Barnabé-Sud (French pronunciation: [sɛ̃ baʁnabe syd]) is a municipality in southwestern Quebec in the Regional County Municipality of Les Maskoutains.

The population as of the 2021 Canadian Census was 962.

It is the birthplace of historian Jean-Baptiste-Arthur Allaire.

On June 7, 2010, police reported that a 20-day-old infant in Saint-Barnabé-Sud had been killed by a dog, a Siberian Husky, that afternoon.

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