Abstract: Herein described is a high strength steel pipe for reinforcing doors of a car, comprising a steel pipe made by seam-welding a steel sheet, wherein a ratio (Hv.sub.1 /Hv.sub.2) of a minimum hardness in a softened area of a weld affected zone to an average hardness in a base material satisfies the following formula,-0.001.sigma.B+1.05.gtoreq.Hv.sub.1 /Hv.sub.2 .gtoreq.-0.003.sigma.B+1.05wherein.sigma.B: tensile strength (kgf/mm.sup.2) andHv.sub.1, Hv.sub.2 : Vickers hardnessand a ratio (.sigma.y/.sigma.B) of a yield strength .sigma.y to a tensile strength .sigma.B of a steel pipe is 0.7 or more.