Recently a new damper system with Kogome truss structure was developed and its mechanical properties were verified basedon the laboratory test. This paper presents a Kagome truss damper external connection method for seismic strengthening of RCframe structural system. The Kagome external connection method, proposed in this study, consisted of building structure, Kagomedamper and support system. The method is capable of reducing earthquake energy on the basis of the dynamic interaction betweenexternal support and building structures using Kagome damper. The pseudo-dynamic test, designed using a existing RC frameapartment for pilot application of LH corporation, was carried out in order to verify the seismic strengthening effects of theproposed method in terms of the maximum load carrying capacity and response ductility. Test results revealed that the proposedKagome damper method installed in RC frame enhanced conspicuously the strength and displacement capacities, and the methodcan resist markedly under the large scaled earthquake intensity level.