The purpose of this paper is to examine the theory of agricultural extension proposed by Liberty Hyde Bailey. L.H.Baily, who presided over the first agricultural extension work in the U. S. at Cornell University Aguricultural Experimental Station in 1894, is the key person in a history of agricultural extension. His goal of the rural education was to build a new rural civilization so that he attached great importance to an extension teaching. He had a strong will to provide the serivce for people. The significant point of his extension theory is that extension work should aid the people to solve thier own problems. I would like to stress that some extension work was done by the cooperation between the college and other agencies.