Henry of Sandomierz (or Henry of Sandomir) (Polish: Henryk Sandomierski) (ca. 1131 – 18 October 1166) was a Duke of Sandomierz since 1138 (titulary) or 1146 (formally) until his death.
He was the fifth but third surviving son of Bolesław III Wrymouth, Duke of Poland, by his second wife Salomea, daughter of Henry, Count of Berg, from whom he received his name.
According to the Testament of his father, Henry inherited the Duchy of Sandomierz, which was at that time in the Seniorate Province of his eldest half-brother and High Duke, Władysław II. Because at the time of Bolesław III's death he was still a minor (1138) the Duchy remained in the Seniorate until he reached the proper age, when Władysław had to given him. But Henry could take formal possession of Sandomierz only when the High Duke was deposed and exiled, in 1146.
As ruler of Sandomierz, Henry appears only on the occasion of the Act of Foundation of a Church in his land. His Ducal title was rarely mentioned by the chronicles, who called him a son of Bolesław III Wrymouth or brother of Bolesław IV the Curly. Some historians (for example M. Gładysz and D. Guttner) advance a hypothesis that he was the “King of the Poles” mentioned by the Greek chronicler John Kinnamos. If the theory were to be correct, Henry would have been the commander of the Polish contingent in the Second Crusade in 1147. This possible incursion in the Crusades was short (if really occur), because in 1149, together with his older brother Bolesław IV, he took part in a military expedition in Kiev to support the Grand Prince Iziaslav II.
The first and maybe the most famous of all Sandomierz's Dukes, Henry certainly ventured to the Holy Land in 1153-1154 (a number of Polish annals reported it under the year 1154 as did Jan Długosz in his Annals) and took part in the Crusade under the command of King Baldwin III of Jerusalem. Henry close affiliation to crusading resulted in the establishment of a commandery of the Hospitallers (between 1154 and 1166) in Zagość.