Mecklenburg-Güstrow was a state of the Holy Roman Empire in Northern Germany, that existed on three occasions ruled by the House of Mecklenburg at Güstrow.

When Magnus died in 1503, his sons Henry V and Albert VII at first ruled jointly over the entire Mecklenburg duchy until its renewed division by the 1520 Neubrandenburg Treaty.

Albert, a fierce opponent of the Protestant Reformation, had insisted on the partition and became duke of Mecklenburg-Güstrow, while his brother Henry retained Mecklenburg-Schwerin.

The controversy was finally decided in 1556 by the Ruppin dictum of Joachim II Hector, Elector of Brandenburg: John Albert I received Schwerin while Ulrich remained Duke of Mecklenburg-Güstrow.

Officially the dukes were reproached for having secretly sided with Christian IV, King of Denmark, while in fact Mecklenburg was given in compensation of the enormous expenses Wallenstein had paid in building up Imperial troops.