Many works have been done on the problem of end cracking in one side welding. To the authors knowledge, however, any attempt has not been successful in practice to change the temperature distribution during welding in preventing this end cracking. In order to establish effective means to prevent this cracking, the present authors carried out a series of experiments on one side welding accompanied by several kinds of countermeasures. They measured the position and length of the crack as well as the expansion of root gap and the final shrinkage across the weld. As a result of these experiments, it was confirmed that the end cracking could be prevented by countermeasures based on mechanical considerations. It was found to be especially effective to heat or cool the plate at proper position during welding.