The task of this paper is the utrasonic testing of test plate welded by MAG welding proces. Ultrasonic testing is one od the most used methods for non – destructive testing of welds. Theoretical part od the papaer describes the propertis of ultrasonic waves, equipment and accessorises used for testing, test techniques and calibration of the test system. Also, an conclusions has been given about adventages and disadventages of utlrasonic testing in relation to other non – destructive methods. Below is a brief description of the MAG welding process and most common errors associated with the described process, such as porosity, lack of fusion and incomplete penetration. In experimental part, the procedure for utlrasonic testing of welded joint of the test plate is described in detail. Testing was performed using the echo - pulse technique, using USM GO ultrasonic device from General Electric company and with tranducer with 60 degree angle. For the calibraiton of the system, the AVG method was apllied. To verify the results, the results of the utrasonic examination were compared with radiographic examination results. It is concluded that the ultrasonic welding test has been successfully performed, and that non-destructive testing methods can be combined and supplemented in order to obtain the most reliable results.