Immunomodulation is a means to modulate an organism's function by antibody production to capture either endogenous or exogenous antigens. We screened single chain antibodies (scFvs) against the extracellular domain of BRI1 (BRI1-LRR), which is known as the binding domain of brassinosteroids, from phage display scFv libraries in order to create plants in which brassinosteroid signaling is impaired by immunomodulation. BRI1-LRR was produced as a fusion protein with GST, and was fixed either on immunotubes by adsorption or on glutathione-Sepharose, against which phages expressing different scFvs, J-1 and J-2, were respectively selected. J-1 showed binding activity to GST-BRI1-LRR fusion protein with clearly lower affinity to GST in ELISA, while J-2 showed higher specificity to GST-BRI1-LRR. In Western blot analysis, J-1, but not J-2, could detect GST-BRI1-LRR, suggesting that J-2 recognizes an epitope formed as a three-dimensional structure of BRI1-LRR.