| The Battle of Sejerø | 
|---|
| Part of The Danish Civil War | 
| | Date | 1132 | 
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 | Location |  | 
|---|
 | Result | Party of Eric Ericson Victory | 
|---|
 | 
| Belligerents | 
|---|
| Forces of Eric | Forces of Magnus | 
| Commanders and leaders | 
|---|
| Eric II of Denmark | Magnus the Strong | 
| Strength | 
|---|
| ~120–240 | ~100–200 | 
| Casualties and losses | 
|---|
| Minor | All but one | 
|  | 
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| Battles of 1131-1134
Clashes between 1139-1143 Battle of LandoraBattle of Bydinge ÅBattle of GlumstrupBattle of Tjutebro
 Battles of 1147-57 Battle of SlangerupBattle of TåstrupBattle of the EiderBattle of ViborgBattle of GedbækThe Danish Småland WarThe Bloodfeast of RoskildeBattle of Grathe Heath
 | 
The battle of Sejerø was a naval battle fought in 1132, near the Island of Sejerø by the Zealandic coast. A zealandic and scanian fleet under Eric II fought a jutlandic fleet under Magnus the Strong. Eric defeated Magnus completely, all that was salvaged from the defeat was the boat Magnus escaped in, the battle was the first defeat dealt to the Niels-Magnus party.