Histone modifications are important components of transcriptional regulation and chromatin-based regulatory processes. In addition, WD40-repeat protein and several other components are involved in these functions. Here we present the development of monoclonal antibodies (MAbs) against Arabidopsis HOS15, a WD40-repeat protein. Mice were immunized with recombinant HOS15 (rHOS15) protein for generating MAbs via the classic hybridoma production technique. We confirmed the specific activity of anti-HOS15 MAbs by tobacco transient expression assays. Based on immunoprecipitation assays, the anti-HOS15 MAb was able to detect endogenous HOS15 in Arabidopsis wild-type plants, but not in hos15 mutant plants. Finally, the anti-HOS15 MAbs are highly sensitive for detecting endogenous HOS15 protein. They can be used for immunological and immunoprecipitation assays to support other experimental strategies. In particular, the anti-HOS15 MAbs will be essential tools to investigate the role of HOS15 in the regulation of tolerance to environmental stresses in plants.