| Henry III | |
| Landgrave of Brabant Count of Louvain Count of Brussels | |
| Spouse: | Gertrude of Flanders |
| Issue: | Adelaide of Louvain Gertrude and others |
| Noble Family: | House of Reginar |
| Father: | Henry II, Count of Louvain |
| Mother: | Adela of Orthen |
| Death Date: | 1095 |
| Death Place: | Tournai |
Henry III of Louvain (German: Heinrich, Dutch: Hendrik, French: Henri; died 1095), was Count of Louvain (Leuven) and Landgrave of Brabant, son of Henry II (c. 1020–1078), Count of Louvain and Brussels, and Adela of Orthen (or Betuwe), a daughter of Count Everard of Orthen.
At his father Henry's death 1078 he became Count of Louvain.
He was allied by family marriages to most of the nearby lords: he was brother-in-law of Baldwin II of Hainaut, and son-in-law of Robert I of Flanders. The bishop of Liège, Henri I of Verdun, was peace-loving. Henry was able to concentrate on the internal affairs of his lands, without external threats. He supported religious foundations in the western parts, and legislated to reduce lawlessness.
After the death on 20 September 1085 of Hermann II, count palatine of Lotharingia, he became landgrave of Brabant, which was an imperial fief between the Dender and the Zenne.
In July 1095, he took part in a tournament in Tournai. Fighting in a joust against Gosuin de Forest, he was mortally wounded.
About 1090 he married Gertrude of Flanders (1080–1117), daughter of Robert I of Flanders and Gertrude of Saxony.
A genealogy of the time attributes to him four daughters (not named). Since he was succeeded by his brother Godfrey I of Leuven, it is inferred that he did not leave a son as heir. It has been suggested that the daughters included:
Gertrude of Flanders, widowed, married in 1096 duke Theodoric II of Lorraine (died 1115) and was mother of Thierry of Alsace ("Theodoric").