A new welding method, called ultrasonic wave tungsten inert gas (TIG) welding, is developed to decrease porosities in a weld. A1050 aluminum plates are welded at an alternating current (AC) frequency from 10 to 40 kHz. An argon (Ar)-1%hydrogen mixture is used as the shielding gas to generate porosities in the experiments. For comparison, a normal TIG welding is also performed at 60 Hz. After welding, the distribution of the porosities in the welds is observed in order to evaluate the effect of the sonic wave. The number of porosities changes with the frequency. A frequency near 15 kHz is the most suitable to decrease the porosities. Using this new method, the area of porosities is decreased to less than about 1/8 of the normal TIG weld. This method is effective for decreasing the number of porosities.