This study investigates the influence of thermal cycle as a result of repeated welding heat input on the mechanical and microstructural properties of the SA516 Gr 65 steel plates weldment in as-welded condition. The test specimens used were having an identical joint design, welded with submerged arc welding (SAW) process. Three different heat inputs of 0.96kJ/mm (low heat input), 1.5kJ/mm (medium heat input) and 3.58 kJ/mm (high heat input) were used for welding three individual specimens. All weld longitudinal tensile testing, Charpy V-notch impact test and weld metal & heat affected zone (HAZ) microstructural testing were done. The work shows that low heat input (LHI) produced welds with highest yield, tensile strength and toughness in the weld metal whereas high heat input (HHI) resulted in decrease in yield, tensile strength and toughness in the weld metal. Increased level of acicular ferrite and a fine grain structure in weldment were achieved with LHI, while the HHI produced coarse grain structure in the weldment and in the HAZ.