Helena of Bulgaria, Empress of Serbia (Bulgarian: , Serbian: ; fl. c. 1315-1374) was a Bulgarian princess, the daughter of Sratsimir of Kran and Keratsa Petritsa and the sister of tsar (emperor) Ivan Alexander of Bulgaria, who married Serbian King and later Emperor Stefan Du?an (r. 1331-55).
Stefan Du?an was crowned King of Serbia at Svr?in on 8 September 1331 (Nativity of the Theotokos). A year later, most likely 26 April 1332 (Thomas Sunday), Du?an married Helena. Previously, it was erroneously assumed that the marriage took place on Easter (19 April), however, marriages are not instituted on Easter in the Orthodox Church. Their wedding night was held at the royal court in Skopje. The marriage was arranged as part of the peace agreement between Bulgaria and Serbia. This marriage provided one son, Stefan Uro? V, and possibly one daughter, Irina. According to John V. A. Fine, she is the same "Irene" who was wife of Gregorios Preljub, the Serbian governor of Thessaly who died in late 1355 or early 1356. They were parents to Thomas II Preljubovi?, Ruler of Epirus from 1367 to 1384. Irene married secondly to Radoslav Hlapen, lord of Kastoria and Edessa.
Helena lived in the Republic of Venice in 1350 and was a regent of Serbia between 1355 and 1356 for her son. On her husband's death, Helena inherited part of Bulgarian lands between the lower Vardar and the Mesta. She also received the Chalcidic peninsula, basing her court at Serres. In 1359 Helena became a nun under the monastic name Jelisaveta (Serbian: ?). However, she continued to play an active role in politics, governing the region of Serres until 1365. After that, she retired from political life, overseeing reconstruction and renovation of several monastic communities, until her death in 1374.