Brentford Ait is a long uninhabited ait (island) in the River Thames. It is on the Tideway near Brentford, in the Borough of Hounslow, London, England.
Brentford Ait has a gap in the middle known as Hog Hole which is apparent at higher tides. In the 18th century there was a notorious pub on Brentford Ait called the Swan or Three Swans, which was closed in 1796. The Swan Steps lead down to the river at Brentford at the site of the crossing to this pub. The ait was planted with trees in the 1920s to screen Brentford's gasworks from the view of Kew Gardens. The ait is covered by willows and alder and is a bird sanctuary with a significant heronry.
| Next island upstream | River Thames | Next island downstream |
| Lot's Ait | Brentford Ait | Oliver's Island |