Objective We investigated the role of glutathione transferase omega 1 (GSTO1) in regulating function of bone marrow-derived dendritic cells (BMDCs).Methods The expression of MHCII on the surface of Gsto1^-/- BMDCs and GSTO1 inhibitor-treated BMDCs was detected by flow cytometry and confocal microscope. To investigate the role of BMDCs, they were cocultured with CD4 T cells from OTII mice in the presence of OVA and IFN-γ production was measured. The recycling and internalization of MHCII molecule in BMDCs treated with GSTO1 inhibitor were measured by flow cytometry. The transcriptional level of MHCII molecule in BMDCs treated by GSTO1 inhibitor was detected by real-time quantitative PCR. The total protein level of MHCII molecule in BMDCs treated by GSTO1 inhibitor was detected by Western blot. The ubiquitination level of MHCII after GSTO1 inhibitor treatment was detected by co-immunoprecipitation assay.Results GSTO1 deficiency and GSTO1 inhibitor did not affect proliferation and apoptosis of BMDCs, but reduced the surface expression of antigen presentation molecule MHCII. Gsto1^-/- BMDCs and BMDCs treated with GSTO1 inhibitor showed impaired CD4 T cell-activating capability. In GSTO1 inhibitor-treated BMDCs, the recycling and internalization of MHCII molecule were normal. GSTO1 inhibitor showed no influence on the transcription of MHCII but reduced its total protein level. Furthermore, BMDCs treated with GSTO1 inhibitor showed higher level of ubiquitinated MHCII molecule and treatment with proteasomes inhibitor MG132 recovered the surface MHCII expression in these cells.Conclusion These data demonstrate that GSTO1 in BMDCs promotes MHCII expression and thus CD4 T cell-activating capacity by inhibiting ubiquitination of MHCII molecule.