| Image Coa: | DEU Gammelby COA.svg |
| Coordinates: | 54.5022°N 9.7967°W |
| Image Plan: | Gammelby in RD.png |
| State: | Schleswig-Holstein |
| District: | Rendsburg-Eckernförde |
| Amt: | Schlei-Ostsee |
| Elevation: | 13 |
| Area: | 8.3 |
| Postal Code: | 24340 |
| Area Code: | 04351, 04355 |
| Licence: | RD |
| Gemeindeschlüssel: | 01 0 58 057 |
| Website: | www.amt-schlei- ostsee.de |
| Mayor: | Marlies Thoms-Pfeffer |
Gammelby is a municipality in the district of Rendsburg-Eckernförde, in Schleswig-Holstein, Germany.