Laser butt-welding of medium carbon steel was investigated using CW 1.5 kW CO2 laser. The effect of laser power (1.2 - 1.43 kW), welding speed (30 - 70 cm/min) and focal point position (-2.5 - 0 mm) on the heat input and the weld-bead geometry (i.e. penetration (P), welded zone width (W) and heat affected zone width (WHAZ)) was investigated using Response Surface Methodology (RSM). The experimental plan was based on Box-Behnken design. Linear and quadratic polynomial equations for predicting the heat input and the weld-bead geometry were developed. The results indicate that the proposed models predict the responses adequately within the limits of welding parameters being used. It is suggested that regression equations can be used to find optimum welding conditions for the desired criteria.