Trarza (Arabic: ولاية الترارزة) is a region in southwest Mauritania. Its capital is Rosso. Other major cities and towns include Mederdra and Boutilimit. Trarza borders the regions of Inchiri and Adrar to the north, Brakna to the east, and the country of Senegal to the south. Its western coastline on the Atlantic Ocean is interrupted only by the Mauritanian capital Nouakchott, which the region completely surrounds.

In 2013, the population of the region was 272,773, compared to 345,076 in 2011. There were 47.79 per cent females and 52.21 per cent males.

In 2008, the activity rate was 42.60 and economic dependency ratio was 0.99. The literacy rate for people aged 15 years and over was 79.0 per cent.