| Arrondissement of Tournai | |
| Native Name: | French: Arrondissement de Tournai |
| Type: | Former arrondissement |
| Coordinates: | 50.6°N 3.4°W |
| Subdivision Type: | Country |
| Subdivision Name: |  Belgium |
| Subdivision Type1: | Region |
| Subdivision Type2: | Province |
| Parts Type: | Municipalities |
| Parts Style: | para |
| P1: | 10 |
| Unit Pref: | Metric |
| Area Total Km2: | 607.52 |
| Population Density Km2: | auto |
| Timezone1: | CET |
| Utc Offset1: | +1 |
| Timezone1 Dst: | CEST |
| Utc Offset1 Dst: | +2 |
The Arrondissement of Tournai (fr|Arrondissement de Tournai; nl|Arrondissement Doornik) is a former arrondissement in the Walloon province of Hainaut, Belgium. It is both an administrative and a judicial arrondissement. However, the Judicial Arrondissement of Tournai also comprises the municipality of Lessines in the Arrondissement of Soignies and all municipalities of the Arrondissement of Ath, with the exception of the municipalities of Brugelette and Chièvres. In 2019 it was merged into the new Arrondissement of Tournai-Mouscron.[1]
The Administrative Arrondissement of Tournai consists of the following municipalities: