The objective of this study is to investigate the structural behavior of beam-to-column connections in which box steel members are used for There are three types in already established beam-to-column connections with box columns for rigid joints, that is diaphragm penetrated type, inside diaphragm type and outside diaphragm type have been developed till now. But it is difficult and is complicated to apply to high rise buildings because of installation of diaphragms under the condition of our country. In this paper the type of beam-to-column connections which is stiffended by triangular plates is tested when box steel members are used for column. Simply bending tests are carried out about this type and its strength is compared with inside diaphragm type.