Ben Gastauer (born 14 November 1987) is a Luxembourgish former professional road cyclist, who rode professionally for the AG2R Citroën Team between 2010 and 2021.

He took three professional victories during his career: the Luxembourgish National Time Trial Championships in 2012, and the general classification and a stage at the 2015 Tour du Haut Var. He was part of the Ag2r–La Mondiale squad that won the team classification and delivered Jean-Christophe Péraud to the podium at the 2014 Tour de France, and part of those which assisted Romain Bardet to podium finishes at the 2016 Tour de France and the 2017 Tour de France. In August 2021 the AG2R Citroën Team announced that Gastauer would retire from competition at the end of the season due to a problem with his pelvic floor, finishing his career at the 2021 Tour de Luxembourg the following month.