Deutscher Kaiser, Tower house in Rhineland-Palatinate, Germany

Deutscher Kaiser is a five-storey late Gothic tower house of slate and tuff at Kastorstraße 3 in Koblenz's old town. Its builder Konrad von Lengenfeld left his coat of arms on a keystone of the star vault in the southern ground floor and in the arched frieze of the north facade.

Konrad von Lengenfeld, a Koblenz magistrate and archiepiscopal mint master, built the tower around 1490; his family had received citizenship in 1486. It later passed to the Anethan family, whose Johann von Anethan served as chancellor under Elector Philipp Christoph von Sötern. In the 19th century it became the inn Zum Deutschen Kaiser, which gave the building its current name.

The building was first called Lengenfeldsches Haus after its builder Konrad von Lengenfeld; the present name comes from the inn Zum Deutschen Kaiser set up here in the 19th century. A restaurant has operated in the tower again since 1 April 2014.

The tower stands at Kastorstraße 3 in Koblenz's old town, a short walk from the Moselle bank and the Kornpforte. It is a protected monument and part of the Upper Middle Rhine Valley UNESCO site, so it is viewed from the street rather than entered as a museum. A restaurant has operated in the building since 1 April 2014.

The tower survived the 1688 bombardment during the War of the Palatine Succession and the World War II air raids, when it was the only building left standing in Kastorstraße after the street was destroyed in 1944. Since then it has stood free, no longer part of a row of houses.