An attempt is made in this paper to explain the construction of 12, 000 gross ton welded tanker in which electric arc welding was incorporated to the extent of nearly 90% a feat never attempted in Japan heretofore. The paper deals mainly on the various phases of material preparation and their dimensional accuracy, as well as, on ground prefabrications and subassemblings, erection and welding sequences, and also, on distortions and contractions produced by the welding. In addition, the construction schedule and the labour aspects are also dealt on. The data contained in this paper has been obtained in actually constructing two vessels of this type, and it is stated in detail, how these findings and actual experience is being applied in the construction of three vessels of the same type now on the shipways under construction.