Hoël II (c. 1031–1084) was Count of Kernev (French: Cornouaille, Breton: Kernev), from 1058 as Hoël V. On the basis of his marriage to Hawise, Duchess of Brittany, in 1066, he became Duke of Brittany jure uxoris.
Hoël was the son of Count Alan Canhiart of Cornouaille and his wife, Judith of Nantes, granddaughter of the illegitimate son of Duke Alan II of Brittany. Hoël started the House of Cornouaille of Brittany, which ruled the duchy until 1156.
Hoël became count of Nantes in 1054. The title came to him from his maternal cousin, Count Matthew I of Nantes, who died in 1050. Alan Canhiart seize the county in Hoël's name in 1050, and ruled it as regent for his son until 1054. Duke Conan II of Brittany attempted to seize Nantes in 1054 but was defeated.
Conan died childless in December 1066 and the duchy passed to Hawise and Hoël, but their marriage may have further strengthened Brittany at a time when external interference was attempted by William the Conqueror. Hawise died in 1072.
During his reign Hoël faced several rebellions from Breton nobles. Geoffrey Grenonat of Rennes (an illegitimate son of Duke Alan III of Brittany and half-brother of Hawise) led a revolt and was joined by Ralph de Gael who had returned to Brittany from England after the failure of the previous year's Revolt of the Earls. In 1076, Ralph having plotted against Hoël, was besieged at Dol. William the Conqueror came to Hoël's aid, after which Hoël finally made peace with Ralph.
Hoël and Hawise had: