Laser welding process is widely used in the industrial area due to its less affects to base metal than general welding. Laser welding has characteristics that highly affect ratio, deeply penetration depth and small heat affected zone(HAZ) due to its in a short time melting and then solidification by a high energy absorption rate. The objective of this research work is to investigate the optimum conditions of a cold rolled carbon steel(SCP1) in a laser welding process using a Nd:YAG laser with a continuous wave(CW). The determination of optimum conditions were performed to change the laser power, beam speed, focus length and then carry out an butt welding. From the results of the investigation, it has been shown that the optimal welding condition without defects in the vicinity of the welded area and with a good welding quality is 1325W of the laser power, 1.4m/min of laser welding speed and 0mm of focus position.