CC motif chemokine receptor 8 (CCR8), a G protein-coupled receptor (GPCR), is highly expressed in regulatory T cells, T helper 2 cells, and cancer cells. It plays important role in allergic inflammation and cancer development. Therefore, specific monoclonal antibodies (mAbs) for CCR8 would be useful for diagnostic and therapeutic purposes of the diseases. However, the production of mAbs for GPCRs has remained very difficult. We have developed a novel method for the development of mAbs, named the Cell-Based Immunization and Screening (CBIS) method. In the present study, an SD rat was immunized with mouse CCR8-overexpressed CHO-K1 cells (CHO/mCCR8). The hybridomas expressing anti-mCCR8 mAbs were screened by using CHO/mCCR8 and CHO-K1 cells. We obtained 73 strongly anti-mCCR8 mAb-expressing hybridomas from 1,916 hybridomas, and we finally established C₈Mab-2 (IgG_2b, kappa). C₈Mab-2 selectively reacted to CHO/mCCR8 cells in a dose-dependent manner, but not to CHO-K1 cells, in flow cytometry. C₈Mab-2 also recognized endogenous mCCR8 in a mouse lymphocyte-like cell line (P388) and a mouse macrophage-like cell line (J774-1). Furthermore, C₈Mab-2 visualized mCCR8 in CHO/mCCR8, P388, and J774-1 cells in immunocytochemistry. In conclusion, we developed the anti-mCCR8 mAb, C₈Mab-2, which is available for detecting endogenous and exogenous mCCR8 in flow cytometry and immunocytochemistry. C₈Mab-2 would be usable for diagnosis and medical treatment for allergic inflammation and cancer in mouse models.