| Grimoald III | |
| Prince of Benevento | |
| Reign: | 788 – 806 |
| Predecessor: | Arechis II |
| Successor: | Grimoald IV |
| Birth Place: | Benevento, Duchy of Benevento |
| Death Date: | 806 (aged 45–46) |
| Death Place: | Southern Italy, probably Benevento |
| Father: | Arechis II |
| Mother: | Adelperga |
Grimoald III (– 806) was the Lombard Prince of Benevento from 788 until his own death. He was the second son of Arechis II and Adelperga. In 787, he and his elder brother Romoald were sent as hostages to Charlemagne who had descended the Italian peninsula as far as Salerno to receive the submission of Benevento. In return for peace, Arechis recognised Charlemagne's suzerainty and handed Grimoald over as a hostage.
When his father and brother both died in 787, Grimoald was allowed to return to Italy. He recognised Frankish overlordship, but was permitted practical independence in return for defending Italy from the Eastern Romans. In 788 he faced a Roman invasion commanded by Adelchis, the son of the last Lombard king, Desiderius. A Frankish army under Winigis and Hildebrand, Duke of Spoleto, joined Grimoald and defeated Adelchis on the coast soon after his landing.
Later, Grimoald tried to throw off Frankish suzerainty, but Charlemagne's sons, Pepin of Italy and Charles the Younger, forced him to submit in 792.