Specially heat-treated low-alloy steel with the 150-170 kg/mm^2 tensile-strength level has been developed recently, and an attempt to apply this steel to solid propellant rocket motor case was undertaken. In this paper are reported some series of fundamental and developmental stage research works on the material properties and on the fabrication techniques. Results of burst test of 450 mm diameter test vessels and pressure test of 1,400 mm diameter test vessel are also shown.