Inactivated vaccines play a pivotal role in preventing avian influenza outbreaks caused by H9N2 viruses. In this study, we employed lovastatin as an adjuvant for a whole-virus H9N2 inactivated vaccine and assessed its immunogenicity in chickens. Immunization effectiveness was evaluated through antibody titers, immune organ indices, phenotypic analysis of T lymphocytes, and RNA-sequencing of the bursa of Fabricius. Results demonstrated that the lovastatin-adjuvanted vaccine (Lov/H9N2) group exhibited significantly higher levels of IgG and hemagglutination inhibition (HI) antibodies compared to the control group. Additionally, enhanced lymphocyte proliferation and increased proportions of CD4+ and CD8+ T cells in the peripheral blood of the Lov/H9N2 group indicated an augmented cell-mediated immune response. RNA-sequencing analysis revealed a significant upregulation of genes related to immune activation in the Lov/H9N2 group, especially in pathways associated with IFN-γ response and chemotaxis. These findings suggest that lovastatin enhances the immunogenicity of the H9N2 vaccine in chickens, positioning it as a potential adjuvant candidate for the poultry industry.