The present invention relates to an repebody capable of binding specifically to interleukin-6 (IL-6) to inhibit the biological activity of IL-6, a polynucleotide encoding the repebody, a vector comprising the polynucleotide, a recombinant microorganism having introduced therein the polynucleotide or the vector, a method of producing the repebody using the recombinant microorganism, a composition for preventing or treating cancer, which comprises the repebody, and a method for preventing or treating cancer, which comprises administering the composition for preventing or treating cancer, which comprises the repebody. The repebody of the present invention significantly reduces the activity of signal transduction and activator of transciption3 (STAT3) and the concentration of interleukin-6, and thus can be widely used as an agent for preventing or treating IL-6-related diseases.