A foldable backrest returning mechanism including a backrest plate and an elastic returning device is disclosed. The backrest plate has a foldable portion. The foldable portion divides the backrest plate at least into a first plate and a second plate. The first plate and the second plate are foldable relative to the foldable portion. The elastic returning device is assembled between the first plate and the second plate, the elastic returning device provides an elastic force to drive the first plate and the second plate to approach each other relative to the foldable portion for making front surfaces of the first plate and the second plate have a returning tendency to approach toward each other. Accordingly, the present invention can prevent arching of the backrest plate at the foldable portion. Furthermore, the present invention provides an infant carrier.