The invention relates to non-destructive ultrasonic testing of flat-bottom rails, laid on track, and can be used for detection of defects in tips of the rail foot on aluminothermic welded joints, performed by the intermediate casting method.During the ultrasonic testing of aluminothermic welded joints, at least two zones for ultrasonic testing were determined with selecting one of at least two zones on the weld bead (reinforcing bead) from the lateral surface of the tip of the rail foot. At least two specific zones are grinded on the weld collar (reinforcing collar) with creation of at least two flat areas, which are able to ensure acoustic contact. The ultrasonic transducer is placed on every flat area of the collar, which is connected to at least one ultrasonic flaw detector. Ultrasonic testing of weld is performed using at least one flaw detector Delta-method or echo-method.As a result of the invention implementation, there is no any “blind zone” in the base of the rail welded joint. The described invention ensures higher accuracy in detection of welds defects within the tips of the rail foot area. 2 z.p. f-ly, 8 il.