The Master Butt welding method was adopted on the construction of Hull No. 24, M. S. “TOSEIMARU”, 5, 000 D. W. T. cargo-boat, for the purpose of shortening the time on the slipway and speeding up the building period. That's to say, two separated hulls (fore and aft, bodies) were built on different slipways, launched individually and then joined each other by the Master Butt Welding method in dry dock. In this report, it is mainly aimed to judge the suitability of this method, by measuring the movement and the stress of the hull occured and the residual stress on the beads of Master Butt Welding which arises in the process of the work. It is also intended herein to estimate the amount of the restriction which the hull will receive from the keel block during joining work of two bo-dies. According to the result of analizing these measurements we may consider that even the greatest blocks such as those of some hundreds tons could be welded and combined together under less restriction, as far as they are treated satisfactorily with perfect welding procedure. In other words, two blocks can be drawn each other by rather small force according to the shrinkage of deposit metal.