Interleukin-13 (IL-13) is a T-cell-derived pleiotropic cytokine of particular medical importance because of its critical role in the development of allergic asthma. The effects of IL-13 on its target cells are mediated through a dimeric transmembrane receptor (IL-13R), which shares the IL-4Rα subunit with the IL-4R system, but contains as a specific component the IL-13Rα1 chain. We have generated a set of single-chain Fv fragments with specific binding capacity to the extracellular domain of the human IL-13Rα1 receptor. Bacteriophage clones displaying receptor-binding antibody domains were selected from both naive and synthetic libraries by repetitive panning on recombinant and cell surface-expressed recombinant IL-13Rα1. Their specific reactivity with native human IL-13Rα1 expressed on the surface of transfected cells was demonstrated by flow cytometry. One binder that specifically interfered with cell activation by IL-13 was extensively characterized. This scFv inhibited IL-13-driven gene transcription and cell proliferation in test cell lines, as well as IL-13-induced activation of primary human monocytes in a dose-dependent manner, with an IC50 below 300 nM. This novel reagent thus constitutes a valuable tool for the further elucidation of IL-13 function in disease and offers potential therapeutic perspectives.