A-TIG welding is a welding method in which TIG welding is conducted by covering a thin layer of activating flux on the weld bead beforehand. The most benefit of this process is the gain in weld penetration depth. A-TIG welds were produced on mild steel plates with TiO2 flux. The emphasis of this paper lies in introducing the effects of various process parameters (welding current, welding speed, powder/acetone ratio of the flux, arc length and electrode angle) in mild steel A-TIG welding. The weld penetration depth was the measured metallographically. An optimum value was determined for each welding parameter.