A6061 aluminum alloy was joined with steel using Zn filler metal under laser irradiation process. The quality of joint was evaluated by the strength of a lap joint. The effects of laser power irradiation conditions such as traveling speed and defocused distance on the joint strength were investigated. The maximum joint strength was obtained at relatively medium laser traveling speed．The excess reaction between filler metal and aluminum formed thick brittle intemetallic compounds between steel and aluminum alloy. The compounds are considered to lead to the reduction in joint strength. It was found that low wetting at high traveling speed and excess reaction layer formation at low traveling speed were responsible for low joint strength. The study revealed that the relatively high joint strength between aluminum alloy and steel was obtained by laser joining method using Zn filler without the use of flux in air atmosphere.