Unterwellenborn is a municipality in the district Saalfeld-Rudolstadt, in Thuringia, Germany. It was created on 1 February 2006 by fusion of the municipalities Birkigt [de], Goßwitz, Könitz, Lausnitz bei Pößneck and Unterwellenborn itself which had cooperated earlier as Verwaltungsgemeinschaft Unterwellenborn. Already on 9 April 1994, the municipalities Dorfkulm, Langenschade and Oberwellenborn had become part of the municipality of Unterwellenborn. In July 2018 the former municipality of Kamsdorf was merged into Unterwellenborn.