Double wall caisson is a type of open dredge caisson applied to the foundations of long span bridges over water, for example, the foundations of Mackinac Strait Bridge in U. S. A., and is now considered to be applied to the foundations for the Bridge interconnecting Honshu with Shikoku in Japan. This report describes the results of our study on the method to build this type of caisson on the shipbuilding berth, and its merits are as follows : (1) The caisson is capable to be built up in laying condition on a berth due to its shallow draft after launching. And as the result of it, remarkable decrease of building time and cost can be achieved. (2) The caisson, whose height is larger than its diametre, can be built up in one body and assembling work at site can be eliminated. (3) The caisson can be easily towed in laying condition compared with upright condition. The fact was found that a small quantity of water poured into the compartments of the double wall could upend the caisson from laying condition to upright condition, due to free water effect in floating body. This phenomenon was investigated experimentalily by models of six different heights, and we obtained diagrams for transitions of the stability curve due to the quantity of the poured water inside of the double wall (see Figs. 8-13), and for critical quantities of poured water to upend the caisson and differences of floating drafts on each floating conditions. (see Figs. 14-16 and Table 1)