Untersteckholz was until December 31, 2009, a municipality in the district Aarwangen the canton of Bern in Switzerland. On 1 January 2010 Untersteckholz has merged with Langenthal Langenthal community.
Untersteckholz is a typical scattered settlement without the village. It is located in the Upper Aargau in the Swiss Plateau, close to the border with the Canton of Lucerne. This is formed from the river red. The neighboring municipalities are Pfaffnau, Melchnau, Busswil at Melchnau, Obersteckholz and Roggwil.