Red-tailed amazons weigh around 425 g (15.0 oz) and are approximately 35 cm (14 in) long. As expected from its common name, it has a broad red band on its tail, but as it largely is limited to the inner webs of the feathers, it is mainly visible from below or when the tail is spread open. Additionally, the tail has a broad yellow tip, and the outer rectrices are dark purplish-blue at the base. The remaining plumage is green, while the throat, cheeks and auriculars are purple-blue, the forecrown is red, and the rectrices are broadly tipped dark blue. It has a yellowish bill with a blackish tip to the upper mandible, a pale gray eye ring, and orange irises. Juveniles have a duller plumage and brown irises.