The strength, rigidity and ductility of the T-stub moment connections are investigated by the experiments. The experiments are consisted of three parts; the simple tension tests of the T-stub and the connection tests with two types of specimens (one for the case of vertical load and the other for the case of lateral load). In this experiments the behaviour of the high strength bolts are mainly investigated, but for the comparison of the fastener, welding and rivets are used. Also the effect of the rib-plate of the T-stub is investigated. The main results are as follows. The high strength bolted T-stub moment connection is good for usual rigid frame, judging from the strength, rigidity and ductility. At the high strength bolted T-stub moment connection, the load at which separation between the connected plates occurs at the bolts is usually smaller than the initial tension of the bolts, under the influence of the flexure of the connected plates. (In this experiments the thickness of the T-stub flange plate is same as the diameter of the bolts, so the separating load of the tension bolts is about 70% of the initial tension of the bolts.) The stiffening effect of the T-stub for the panel zone of the beam-to-column connection, which is very important part of the steel skeleton in the case of lateral load, is not so great. The effect of the rib-plate of the T-stub is not so significant.