Wietze () is a river of Lower Saxony, Germany, a tributary of the Aller. Its total length including its source river Edder (length ) is .
The river begins at the confluence of the Edder and Flöth northeast of Hanover near , a district of Isernhagen. From there it flows several kilometres to the west through the southern part of Isernhagen to Langenhagen and from there on only in a northern direction to just beyond the village of Wietze, where it merges with the River Aller flowing from the south.
In the second half of its course the Wietze forms a pronounced depression with a bog-like region known as the Wietzenbruch. This is a region of extensive forest and fen woodland (Bruchwald) about in area. Wietzenbruch, a suburb of the town of Celle lies next to it.
The name of the river is derived from ("wych elm river").