After a period of being left out of the side altogether, Ainsworth moved on loan to fellow League One side Brentford on 27 January 2010. He made his debut in the 4–0 win over Gillingham at Griffin Park on 6 February 2010. After making his first start for the Bees, against Yeovil in April 2010, he got in trouble with the club's manager Andy Scott, having gone straight down the tunnel after being substituted. Afterwards Scott said that Ainsworth wouldn't play for the club again for showing disrespect to the club and its fans, and he was sent back to Huddersfield.