Abstract: Development of -50℃ level low-temperature seamless steel tubes for pressure vessels is descrbied. The comprehensive properties of the above-mentioned steel tubes, produced using the newly-developed steel B651 with the process of open-hearth smelting→ladle refining or the process of arc-furnace smelting→ladle refining with Ar injection, followed by temperature-controlled rolling, are all over the values specified by the experiment task sheet, having its low-temperature impact energy 5 times higher than that specified by JIS G3460-84.