Residual stresses exist in all manufacturing processes such as casting, machining and welding in which heat and/or force is used. Aluminum due to its high shrinkage and expansion and the need to use high heat and loss of properties in the adjacent areas of the welding line, has many disadvantages and defects after welding compared to other metals. On the other hand, many strength-enhancing operations are not practical because of the sensitivity of aluminum metal to heat. The ultrasonic peening treatement (UPT) is a newly developed and inexpensive method that improves, welded joints and stractures strength by applying low amplitude and high frequency oscillations. In order to investigate the effect of ultrasonic peening treatement, in this study, Al6061-T6 sheets with 3 mm thickness were welded by pulsed and direct current condition with tungsten inert ga(TIG)welding. Ultrasonic peening was then applied to the weld toe with the power of 500 and 800 watts. Metallographic, residual stress, micro hardness, tensile stress and slow strain rate tests (SSRT) were performed on Al6061-T6 welding joints with and without ultrasonic peening treatement. Using this method, the tensile residual stresses were eliminated and the compressive residual stresses of 199 MPa at 500 W and 250 MPa at 800 W were replaced. Surface hardness increased from 79 to about 129 Vickers. The distribution and geometry of the secondary particles phases in the metal, which are the main determinants of the strength of the selected metal, have changed. The tensile strength of the heat-affected area was also greater than that of the base metal. Keywords: UPT, TIG, residual stress, SSRT, secondary particles phases,