The Memminger Ach (or seldom Memminger Aach) is a river of Bavaria, Germany.
The Memminger Ach is a tributary of the Iller, part of the Danube river system and forms an important part of the landscape in the town of Memmingen. The river is 19.2 km (11.9 mi) long (36.0 km (22.4 mi) including its source river Kressenbach). It flows into the Iller near Pleß.