A device for air interlacing (10) of a yarn (Y), comprising an interlacing chamber (24), a first entrance channel (22) for receiving the yarn (Y) at the device (10) entrance and feeding it to the interlacing chamber (24), and a second exit channel (23) for receiving the yarn from the interlacing chamber (24) and releasing it at the device exit, in which the interlacing chamber (24) is delimited by a first emitting wall (24a) bearing a nozzle (26) for the emission of a continuous jet of compressed air (31), and a second deflecting wall (24b), opposite the first wall (24a), suitable for receiving and deflecting the jet of compressed air (31) emitted by the nozzle (26) and intersecting the yarn to be interlaced, and in which the second deflecting wall (24b) is concave in shape both on a transversal plane and on a longitudinal plane with respect to the feeding path (11) of the yarn (Y) through the device.