The seismic capacity of beam-to-column connections in steel high-rise frames is a matter of concern, particularly when they are subjected to long-period ground motions. A previous full-scale shaking table test conducted at E-Defense disclosed cracks and fractures in such beam-to-column connections. This paper examines the effects of three types of beam-to-column connection retrofit: supplemental welds, wing plates, and a haunch. The performance of a total of twenty-eight connections tested by the shaking table tests is evaluated. When the supplement welds are further applied to the web-to-column connection, the cumulative plastic rotation capacity is increased to eight times that of the connection without retrofit. For the wing plate and haunch connections, the critical section is moved from the beam end to the beam cross-section corresponding to the tip of the wing plates or the haunch, resulting in significant improvement of ductility by eight times that of the un-retrofitted connection.