In this study, AISI 1020 plate of 6 mm thickness has been welded by autogenous TIG welding process maintaining different root gap (0, 0.5, 0.75 and 1 mm). The weld bead profile and the tensile strength of the welded joint has been analysed. From the experimental results it is revealed that, for increasing the root gap, weld depth penetration increases; whereas weld bead width and heat affected zone (HAZ) is almost uniform. However, at the similar condition, under-filling of the weld joint increases with the increase in root gap. For using 1 mm root gap, weld joint exhibit full depth of penetration and maximum tensile strength, along with higher under-filling.