On 31 May 1700, he married his first wife, Louise Dorothea, Princess of Prussia (1680–1705), daughter of Frederick I of Prussia (1657–1713) and Elizabeth Henrietta of Hesse-Kassel (1661–1683).
Louise Dorothea died in childbirth in December 1705.

His second wife, whom he married in 1715, was Ulrika Eleonora, Princess of Sweden,  (1688–1741), daughter of Charles XI of Sweden (1655–1697) and of Ulrika Eleonora of Denmark (1656–1693).
Ulrika suffered two miscarriages, one in 1715 and another in 1718, after which there are no further recorded pregnancies.

Frederick I had three extramarital children with his mistress Hedvig Taube:
Frederick William von Hessenstein (1735–1808).

Charles Edward von Hessenstein (1737–1769).

Hedwig Amalia von Hessenstein (1743–1752).

After the death of Hedvig Taube, his official mistress was the noblewoman Catharina Ebba Horn, whom he gave the title and recognition of German-Roman Countess (1745–1748).

Thus, the Hessian line in Sweden ended with him and was followed by that of Holstein-Gottorp.
In Hesse-Kassel, he was succeeded by his younger brother William VIII, a famous general.
On 31 May 1700, he married his first wife, Louise Dorothea, Princess of Prussia (1680–1705), daughter of Frederick I of Prussia (1657–1713) and Elizabeth Henrietta of Hesse-Kassel (1661–1683). Louise Dorothea died in childbirth in December 1705.
His second wife, whom he married in 1715, was Ulrika Eleonora, Princess of Sweden,  (1688–1741), daughter of Charles XI of Sweden (1655–1697) and of Ulrika Eleonora of Denmark (1656–1693). Ulrika suffered two miscarriages, one in 1715 and another in 1718, after which there are no further recorded pregnancies.
Frederick I had three extramarital children with his mistress Hedvig Taube:
Frederick William von Hessenstein (1735–1808).
Charles Edward von Hessenstein (1737–1769).
Hedwig Amalia von Hessenstein (1743–1752).
After the death of Hedvig Taube, his official mistress was the noblewoman Catharina Ebba Horn, whom he gave the title and recognition of German-Roman Countess (1745–1748).
Thus, the Hessian line in Sweden ended with him and was followed by that of Holstein-Gottorp. In Hesse-Kassel, he was succeeded by his younger brother William VIII, a famous general.
Frederick I of Sweden