In the present work, the effect of welding current and electrode negative (EN) ratio on microstructure and mechanical properties of square groove butt joint produced by alternating current gas metal arc welding (AC-GMAW) process has been investigated. The experiments were conducted using different combination of welding current ranging from 150 A to 250 A with three distinct EN ratios i.e., 0%, 30% and 50% on 5 mm thick steel plates at a constant joint gap of 1 mm and welding speed of 10 mm/s. The effect of current and EN ratio on welding soundness was evaluated through optical microscopy, tensile tests and micro-hardness mapping. The results revealed that, at higher values of currents, an increase in EN ratio resulted an increase in penetration depth. It was found that at a current of 250 A and a 50% EN ratio, the deep penetration was obtained. Tensile test results showed that the tensile strength properties improved with increasing current. Furthermore, the micro-hardness distribution was not strikingly affected by changing the EN ratio.