Abstract: It is generally believed that column transverse stiffeners (also known as continuity plate) will be beneficial to the ductility of the welded beam-to-column connections and the AISC Seismic Provisions for Structural Steel Buildings recommend the use of continuity plates in the column unless tests show that the connection will work without them. The provisions are questionable as many T-shaped connection specimens with continuity plates show little ductility while connections without continuity plates exhibit satisfactory ductility. To further investigate the effects of continuity plates on the ductility of T-shaped connections, nonlinear analysis of welded beam-column connections under both monotonic loading and cyclic loading was performed in the paper. Several mechanical parameters were employed to assess the ductility of the connections. These quantities were sampled at weld-beam flange interface where the stress conditions were more critical at higher plastic rotation. The finite element analysis indicated that the plastic strain at the weld-beam tension flange interface was significantly increased due to the presence of continuity plates, which might cause a great reduction of ductility. Consequently, the analytical results demonstrated that the continuity plate located on both sides of column web was one of mains causes which contributed to brittle failure of T-shaped exterior connections under seismic loading. The conclusion drawn from the paper was verified against experimental data available in the literature.