Theosebia, also known as Theosebia the Deaconess is a 4th century female christian, a saint in the Eastern Orthodox. As a saint she is referred as Blessed Theosebia the Deaconess.

Her life and identification is ambiguous: nor birth year and dead year are uncertain (probably subsequent to 381). But she played assumingly an important role in the church in Nyssa where she was called diaconissa, the deaconess.

Cyril of Jerusalem wrote a letter of condolence on her death to Gregory of Nyssa in which Cyril mentioned her "your sister Theosebia" and "true consort of a priest". Hither comes the ambiguity of her identification. Some historians supposed Theosebia was the wife of Gregory of Nyssa, others suppose she was one of his sisters as same as Macrina the Younger, then Theosebia was the sister of Basil the Great too. Others imagined that she was the wife of Gregory Nazianzen, but there is no evidence to show that he was ever married.