List of state leaders in 1551

Africa

Empire of Ethiopia - Gelawdewos (1540–1559)
Kingdom of Kongo - Diogo I, Manikongo (1545–1561)
Kingdom of Sennar -
1. Nayil (1533/4 - 1550/1)
2. Abd al-Qadir I (1550/1 - 1557/8)
Songhai Empire - Askia Daoud, Askia of the Songhai Empire (1549–1582)

Sultanate of Aceh, Alauddin al-Kahar (1539–1571)
China (Ming Dynasty) - Jiajing Emperor (1521–1567)
Jaffna Kingdom - Cankili I (1519–1561)
Japan (Sengoku period)
- Monarch - Emperor Go-Nara (1526–1557)
- Shogun (Ashikaga) - Ashikaga Yoshiteru (1546–1565)
Korea (Joseon Dynasty) - Myeongjong (1545–1567)
Mughal Empire - Ibrahim Sur (1545–1555)
Ryūkyū Kingdom - Shō Sei (1527–1555)
Sulu Sultanate - Sultan Nasir ud-Din I (1548–1568)
Vijayanagara Empire - Rama Raya (1542–1565)

Kingdom of Denmark and Norway - Christian III (1534–1559)
- Duchy of Schleswig - Adolphus (1544–1586), Christian III (1523–1559), and John II (1544–1580) in condominial rule
Kingdom of England - Edward VI (1547–1553)
Kingdom of France - Henry II (1547–1559)
Holy Roman Empire - Charles V (1519–1556)
- Duchy of Holstein - Adolphus (1544–1586), Christian III (1523–1559), and John II (1544–1580) in condominial rule
Hungary -
- Royal Hungary - Ferdinand I (1526–1564)
- Eastern Hungarian Kingdom - John II Sigismund Zápolya (1540–1571)
Polish–Lithuanian union - Sigismund II, Grand Duke of Lithuania (1544–1572) and King of Poland (1548–1572)
Kingdom of Navarre - Henry II d'Albret (1516–1555)
Ottoman (Turkish) Empire - Suleiman the Magnificent (1520–1566)
Kingdom of Portugal - John III the Pious (1521–1557)
Grand Duchy of Moscow - Ivan IV the Terrible, Grand Prince of Moscow (1533–1547) then Tsar of Russia (1547–1584)
Duchy of Savoy - Charles III (1504–1553)
Kingdom of Scotland - Mary, Queen of Scots (1542–1567)
Kingdom of Spain - Charles I (1516–1556)
Kingdom of Sweden - Gustav I Vasa (1521–1560)
Republic of Venice - Francesco Donato, Doge of Venice (1545–1553)
Principality of Wallachia - Mircea the Shepherd, Voivode of Wallachia (1545–1552)