Dossou Agadja was the fifth King of Dahomey. He succeeded Houessou Akaba, and ruled from 1708 to 1732.

Akaba's only son, Agbo Sassa , was only ten years old when Akaba died, so as Akaba's brother, Agadja took the throne to become the fifth king. He refused to let Agbo Sassa reclaim the throne when he came of age and forced him into exile.

Agadja's reign was characterized by continual warfare. The Yoruba soldiers of the kingdom of Oyo defeated the army of Abomey; Agadja parlayed peace terms including the payment of tribute. For the next hundred years, the Kingdom of Abomey paid the King of Oyo an annual tribute in young men and women destined for slavery or death in ceremonies, as well as cloth, guns, animals and pearls.

The kingdom of Abomey grew during Agadja's reign, however; it conquered Allada in 1724, and in 1727 conquered the kingdom of Savi , including its major city, Ouidah. Agadja's victory over Ouidah came in part as a result of his use of a corps of women shock-troopers, called Dahomey Amazons by the Europeans after the women warriors of Greek myth, in his army. The Amazons became a dynastic tradition. When Abomey conquered Savi and Ouidah, it gained direct access to the sea and took over the lucrative slave trade with the Europeans. As a result, Agadja's symbol is a European caravel boat.

Agadja was succeeded by Tegbessou.