| Arni | |
| Name Local: | Άρνη |
| Type: | municipal unit |
| Periph: | Thessaly |
| Periphunit: | Karditsa |
| Population: | 2140 |
| Population As Of: | 2021 |
| Area: | 89.2 |
| Coordinates: | 39.4°N 26°W |
| Postal Code: | 433 00 |
| Licence: | ΚΑ |
Arni (Greek, Modern (1453-);: Άρνη) is a former municipality in the Karditsa regional unit, Thessaly, Greece. Since the 2011 local government reform it is part of the municipality Sofades, of which it is a municipal unit.[1] The municipal unit has an area of 89.185 km2.[2] Population 2,140 (2021). The seat of the municipality was in Mataragka. It was named after the ancient Aeolian town of "Arne" (Greek, Ancient (to 1453);: Ἄρνη), which was located near present Mataragka.[3]