Styrbjarnar þáttr Svíakappa (The Tale of Styrbjörn the Swedish Champion) is a short story, a þáttr on the Swedish claimant and Jomsviking Styrbjörn the Strong preserved in the Flatey Book (GKS 1005 fol 342-344, ca 1387-1395).

It is inserted together with Hróa þáttr heimska in the description of Olaf Haraldsson's wooing of the Swedish princess Ingegerd Olofsdotter.

Their purpose appears to be to present the Swedish court, its traditions and Þorgnýr the Lawspeaker.

In the story, Styrbjörn becomes the leader of the Jomsvikings and makes war against the Danes, until he makes peace with the Danish king Haraldr Gormsson who in return gave Styrbjörn his daughter and 100 ships.

When the forces meet, Þorgnýr the Lawspeaker has created an ingenious war machine by tying horses and cows together with spears and spikes.