The canton of Saint-Omer-Sud is a former canton situated in the department of the Pas-de-Calais and in the Nord-Pas-de-Calais region of northern France. It was disbanded following the French canton reorganisation which came into effect in March 2015. It had a total of 21,597 inhabitants (2012).

The canton is organised around Saint-Omer in the arrondissement of Saint-Omer. The altitude varies from 0m (Saint-Omer) to 119m (Wizernes) for an average altitude of 38m.

The canton comprised 4 communes:

• Longuenesse
• Saint-Omer (partly)
• Tatinghem
• Wizernes

• Cantons of Pas-de-Calais
• Communes of Pas-de-Calais
• Arrondissements of the Pas-de-Calais department

50°43′55″N 2°13′59″E / 50.73194°N 2.23306°E / 50.73194; 2.23306