The purpose of this paper is to evaluate the behavior of reinforced concrete columns strengthened by section enlargement in consideration of long-term deformation. Experimental variables considered in this study are sustained-loading and new casting materials. Long-term deformation test and static loading test have been carried out on 7 types of specimens. The test results show that outer reinforced concrete column does not greatly influence the long-term deformation of inner reinforced concrete column due to creep and the column specimen under lower sustained load has larger load bearing capacity than that under larger sustained load.