Al coated steel sheets with excellent heat resistance,thermal reflection,and corrosion resistance are widely used in various applications.The laser weldability of the Al coated steel sheet for full penetration welding was reported.The phenomenon caused by intermixed aluminum and behavior of aluminum in the weld were investigated.Al coated steel sheets that have various thickness and coating mass were prepared for laser welding.The effects of parameters such as welding conditions and Al coating conditions were investigated.Al content mixed in the weld after laser welding was evaluated,and then a correlation between the mixed Al and mechanical properties was investigated.The results show that the Al-rich zones which have Fe-Al intermetallic compounds are found in the weld.The intermetallic compounds cause the decreased strength of the weld. Al coated steel sheets with excellent heat resistance, thermal reflection, and corrosion resistance are widely used in various applications. Laser weldingability of the Al coated steel sheet for full penetration welding was reported. The phenomenon caused by intermixed aluminum and behavior of aluminum in the weld were investigated .Al coated steel sheets that have various thickness and coating mass were prepared for laser welding. these effects of parameters such as welding conditions and coating conditions were investigated. Al content mixed in the weld after laser welding was evaluated, and then a correlation between the mixed Al and mechanical properties was investigated. The results show that the Al-rich zones which have Fe-Al intermetallic compounds were found in the weld. The intermetallic compounds cause the decreased strength of the weld.