| Alster | |
| Pushpin Map: | Bavaria |
| Pushpin Map Caption: | Location of mouth in Bavaria |
| Mouth Location: | Itz |
| Mouth Coordinates: | 50.1294°N 10.8711°W |
| Subdivision Type1: | Country |
| Subdivision Type2: | States |
| Subdivision Name2: | Bavaria and Thuringia |
| Length: | 20.7km (12.9miles) |
The Alster is a river of Bavaria and of Thuringia, Germany. It is a right-bank tributary of the Itz, which it joins near Kaltenbrunn.