| Official Name: | Kostanjek |
| Pushpin Map: | Slovenia |
| Pushpin Label Position: | left |
| Pushpin Map Caption: | Location in Slovenia |
| Subdivision Type: | Country |
| Subdivision Name: | Slovenia |
| Subdivision Type1: | Traditional region |
| Subdivision Name1: | Styria |
| Subdivision Type2: | Statistical region |
| Subdivision Name2: | Lower Sava |
| Subdivision Type3: | Municipality |
| Subdivision Name3: | Krško |
| Area Total Km2: | 2.97 |
| Population As Of: | 2002 |
| Population Total: | 135 |
| Population Blank1 Title: | Ethnicities |
| Population Blank2 Title: | Religions |
| Coordinates: | 46.009°N 15.5414°W |
| Elevation M: | 337.7 |
| Postal Code: | 8272 |
| Footnotes: | [1] |
Kostanjek (pronounced as /sl/, de|Kosteinek[2]) is a settlement north of Zdole in the Municipality of Krško in eastern Slovenia. The area is part of the traditional region of Styria. It is now included with the rest of the municipality in the Lower Sava Statistical Region.[3]
The local church is dedicated to Saint Vitus and belongs to the Parish of Zdole. It is a Baroque church dating to the early 18th century. Its nave was extended in 1853.[4]