Stephen Ostojić (Bosnian: Stjepan Ostojić/Стјепан Остојић) was King of Bosnia from 1418 until 1421.
A member of the House of Kotromanić, Ostojić was the only legitimate son of King Stephen Ostoja of Bosnia, born by his second wife, Kujava Radinović. His illegitimate half-brothers were King Stephen Thomas of Bosnia and anti-king Radivoj Ostojić.
He assumed the crown of Bosnia upon the death of his father in 1418, three years after his parents' divorce. One of his first acts was the imprisonment of his stepmother, Jelena Nelipčić, under the influence of his mother. Queen Jelena died in prison under unclear circumstances, her death probably having been ordered by Queen Kujava.
In 1419, the young King reconfirmed the alliance of the Kingdom of Bosnia and the Republic of Venice. However, he failed to strengthen his royal authority among the nobles. The alliance with Venice did not help him keep his crown; in 1420, his half-uncle, the former King Stephen Tvrtko II of Bosnia, returned to Bosnia. By 1421, Ostojić was deposed by Tvrtko II with the help of the Ottoman Empire.
Ostojić disappears from historical record after his deposition.
| Regnal titles | ||
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| Preceded by Stephen Ostoja |
King of Bosnia 1418–1421 |
Succeeded by Stephen Tvrtko II |
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