| Rantzau | |
| Native Name Lang: | de |
| Settlement Type: | Amt |
| Subdivision Type: | Country |
| Subdivision Name: | Germany |
| Subdivision Type2: | State |
| Subdivision Name2: | Schleswig-Holstein |
| Subdivision Type3: | District |
| Subdivision Name3: | Pinneberg |
| Seat Type: | Region seat |
| Seat: | Barmstedt |
| Leader Title: | Amtsvorsteher |
| Leader Name: | Matthias Bagger |
| Area Total Km2: | 112.0 |
| Population Total: | 8,905 |
| Population As Of: | 2020-12-31 |
| Website: | www.amt-rantzau.de |
Rantzau is an Amt ("collective municipality") in the district of Pinneberg, in Schleswig-Holstein, Germany. It is situated around Barmstedt, which is the seat of the Amt, but not part of it. The Amt was named after the County of Rantzau, which existed between 1649 and 1864.
The Amt ("collective municipality") Rantzau consists of the following municipalities: