| Catherine | |
| Native Lang1 Name1: | Єкатерїна |
| Augusta | |
| Succession: | Byzantine Empress consort |
| Reign: | 1057–1059 |
| Consort: | yes |
| Spouse: | Isaac I Komnenos |
| Father: | Ivan Vladislav of Bulgaria |
| Mother: | Maria |
Catherine of Bulgaria (Church Slavic; Old Slavonic; Church Slavonic; Old Bulgarian; Old Church Slavonic: Єкатерїна, Greek, Modern (1453-);: Αἰκατερίνη|Aikaterini, Bulgarian: Екатерина|Ekaterina; died after 1059) was empress consort to Byzantine emperor Isaac I Komnenos and co-regent of Constantine X for a period after the abdication of her spouse in 1059. She was a daughter of Ivan Vladislav of Bulgaria and his wife Maria, and thus a sister of Presian and Alusian. Catherine was also a paternal aunt of Maria of Bulgaria.
Catherine was a daughter of Ivan Vladislav (reigned 1015–18), the last Tsar of Bulgaria. She married the general Isaac Komnenos. After he became emperor in 1057, Isaac raised her to Augusta.
Isaac abdicated the throne on November 22, 1059. He retired to the Stoudios Monastery and spent the remainder of his life, until his death in late 1060 or 1061, as a monk. Following her husband's abdication, she appears to have co-reigned for a while with Constantine X, but eventually she too retired to the Myrelaion monastery under the monastic name of Xene.
Catherine had at least two children with Isaac: