[en] This paper describes on the manufacturing system for nuclear grade steel materials at Mizushima Works of Kawasaki Steel Corporation. This works has developed the manufacturing system by using a ladle refining furnace (LRF), and obtained the ASME quality system certificate for thick plates and forgings of nuclear grade. The impurity content of raw material is regulated, and the contents of As, Sb, Cu and S are kept at minimum. In the convertor refining, dephosphorization is carried out thoroughly. Then, the second refining and the degasing treatment are carried out in the LRF. The chemical composition of the refined steel is shown in a table which shows very low content of harmful elements. The result of measurement of the rise of transition temperature (Tr 30) by neutron irradiation was good. The characteristic features of the rolling works are smoothness of lay-out, computer control and automatic operation, and an ultra-powerful rolling machine. The manufactured plates show good accuracy of thickness and smooth plate surface. Forging and heat treatment for plates and forgings are made. The quality system manual of this works is written according to the requirement of ASME code. The certified material test report (CMTR) is issued for shipped material. The person in charge of non-destructive test is authorized according to the ASNT Recommended Practice No. SNT-TC-1A (1975). (Kato, T.)