Bad Nenndorf (Northern Low Saxon: Nenndörpe) is a small town in the district of Schaumburg, Lower Saxony, Germany.

The sulphur springs, which until then had been despised as devil's excrement on account of their pungent odour, were reckoned among the most powerful in Europe, and could now finally be applied with great success for rheumatism, arthritis and skin complaints.

In 1866 Bad Nenndorf became the Royal Prussian state spa, and financial support from Berlin enabled it to expand further.

It lies on the northern edge of the Mittelgebirge (central uplands), on the Hellweg, a route between Rhine and Elbe which had been used for centuries.

Towards the end of the Second World War, the town served as the headquarters of the U.S. 84th Infantry Division under Major-General Alexander R. Bolling.

Between June 1945 and July 1947, Bad Nenndorf was the site of a British Combined Services Detailed Interrogation Centre (CSDIC) center through which several hundred Nazi and suspected Communist prisoners passed.