To obtain an oligomer reagent useful in the use similar to that of an antibody and provide a method of preparing the oligomer reagent.

The oligomer reagent is an antibody-like reagent or an oligomer which comprises a natural or derived oligonucleotide selected by a method based on high specificity but not high affinity and is derived from a synthetic oligonucleotide. The oligomer reagent exhibits unusual ability similar to natural polyclonal or monoclonal antibodies in many uses and is useful in all uses (e.g. Western blot, immunoprecipitation, immunocytodyeing, radioimmunity assay, ELISA, medicine for disease, microtray for diagnosis or the like) participating in the recognition of nondenatured and/or denatured proteins.