With the recent construction of large size oil-tankers and ore carriers, the routes already constructed have become narrower and its depth of water are now insufficient for the pass of these large-size ships.
　At present, for the removal of dangerous unsunken rocks dotted in the Inland Sea of Seto, Kanmon Region and other routes, various types of rock breaker is used.
　In this report, the authors present the result of the analyses on the performance test by the rock breaker barge Ozuchi-Go carried out at the shore Kurohana-No-Iso in the Inland Sea of Seto to get the efficiency of rock breaker barge and some data for the desing of large-size rock breaker barge.
　The barge Ozuchi-Go is a new type rock breaker barge with dozer on its bow, the width of which is 6m, the weight of its breaker is 30ton, the principal dimension is L=33.68m, B=13.0m, D=3.0m, d=2.1m.
　Through this investigation on this barge, the relation between the dropping height, the frequency of dropping and interpenetration depth, and the relation between dropping height for the maxmum inter-penetration depth for each dropping were confirmed.
　The penetration depth by the dropping of rock breaker is expressed by the function as the crash coefficient tanβ1(increase incline of cumulative total of interpenetration depth) and d' n=1 (corresponding interpenetration depth by one dropping).
　The authors also present the way of measurement on the crash coefficient and examined on the relation between crash coefficient and the crash operation efficiency and some problems on the rock breaker equipments and suggested some new design method on the rock breaker.