Bertha de Blois was born circa 1015 in Blois, Loir-et-Cher, Centre-Val de Loire, France to Odo II de Blois (c983-1037) and Irmengarde d'Auvergne (c995-1040) and died 11 April 1085 Chartres, Ille-et-Vilaine, Bretagne, France of unspecified causes. She married Alain III de Bretagne (997-1040) 1018 JL . She married Hugues IV du Maine (c1006-1051) 14 May 1046 JL .
Children
| Name | Birth | Death | Joined with |
| Conan II de Bretagne (1030-1066) | 1033 | 11 December 1066 | |
| Havoise de Bretagne (1027-1072) | 1027 | 1072 | Hoël de Cornouaille (c1027-1084) |
| Name | Birth | Death | Joined with |
| Marguerite du Maine (c1045-1063) | 1045 | 1063 | |
| Herbert II du Maine (c1048-1062) | 1048 | 1062 | |