In most cases, anti-protein aptamers are selected by systematic evolution of ligands by exponential enrichment (SELEX) using purified recombinant protein targets. Cell surface proteins, however, are not easy targets for SELEX due to the difficulties associated with their purification. Here, we developed a novel SELEX procedure (referred to as TECS-SELEX) in which cell-surface displayed recombinant protein is directly used as the selection target. Using this method, we isolated RNA aptamers against transforming growth factor-beta type III receptor expressed on Chinese hamster ovary (CHO) cells. One of the RNA aptamers has a dissociation constant in the 1 nM range and competed with transforming growth factor-beta to bind to the cell surface receptor in vitro.