A hybrid laser system which combines preheating with a blue diode laser with welding with a single mode fiber laser was developed to realize a highly efficient laser welding of copper. With the hybrid laser system, the blue diode laser and the single mode fiber laser were combined coaxially and a stair shape beam profile was formed at the processing point. Each laser was irradiated to a copper sample and the output power of the blue diode laser was varied to investigate an effect of preheating with it on the welding with the single mode fiber laser. The melting and solidification dynamics of copper was evaluated with a high speed video camera and a thermo camera. As the results, it was found that the melting volume of copper and the temperature at the processing point increased by preheating with the blue diode laser. The copper wire with 2.0×3.5×50 mm was weld in 0.3sec by using hybrid laser with 1kW single mode fiber laser and 200W blue diode laser. Thus, it was concluded that a highly efficient welding of copper was achieved with the preheating with the blue diode laser.