In this study, 304L stainless steel was bonded by MIG welding and mechanical and microstructural properties of the welded samples were investigated. Welding was carried out under different shielding media, which are argon and different additions of hydrogen in Ar. As current values, 140, 180 and 240 A were chosen for the welding current parameters. The sample that was welded under 1.5% H-2-Ar shielding media and with a welding current of 240A was found to be the best in terms of means of tensile strength. Impact tests revealed that toughness of the welding increases with increasing hydrogen amount in Ar and welding current. For all the welding parameters, hardness test results showed that base metal gave a higher hardness value than HAZ and weld metal. Welded samples were also characterized by means of bending test and microscopic investigations. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.