The 1978 Mercedes Cup, was a men's tennis tournament played on outdoor clay courts and held at the Tennis Club Weissenhof in Stuttgart, West Germany that was part of the 1978 Grand Prix circuit. It was the inaugural edition of the tournament and was held from 17 July until 23 July 1978. Unseeded Ulrich Pinner won the singles title.
Ulrich Pinner defeated 
Kim Warwick, 6–2, 6–2, 7–6
Tomáš Šmíd / Jan Kodeš defeated 
Carlos Kirmayr / Belus Prajoux, 6–3, 7–6