Long-tailed Sylph
Aglaiocercus kingii
- Least concern
- Card rarity: Common
- Birds

The long-tailed sylph is a species of hummingbird in the "coquettes", tribe Lesbiini of subfamily Lesbiinae. It is found in Bolivia, Colombia, Ecuador, Peru, and Venezuela.
Classification
- Class
- Aves
- Order
- Apodiformes
- Family
- Trochilidae
- Genus
- Aglaiocercus