Human adenovirus type 55 (HAdV-55) is an emerging respiratory pathogen associated with severe pneumonia, for which no licensed vaccines are currently available. The lack of physiologically relevant small-animal models has limited preclinical evaluation of vaccine candidates. In this study, we generated a transgenic mouse model co-expressing human CD46 and desmoglein-2 (DSG-2), key entry receptors for HAdV-55, and evaluated its utility for vaccine efficacy testing. A bicistronic expression system enabling simultaneous expression of CD46 and DSG-2 was constructed and functionally validated in vitro, demonstrating enhanced susceptibility to HAdV-55 infection. The transgenic mice exhibited dose-dependent weight loss, robust viral replication in lung tissues, and characteristic histopathological changes following intranasal challenge, recapitulating key features of human adenoviral pneumonia. Using this model, we assessed the immunogenicity and protective efficacy of an inactivated HAdV-55 (iHAdV-55) vaccine formulated with alum. Vaccination induced strong HAdV-55-specific IgG and neutralizing antibody responses, which increased over time following prime–boost immunization. Upon viral challenge, vaccinated mice showed significantly reduced weight loss and accelerated recovery compared to controls. Viral load analysis demonstrated effective control of viral replication and clearance in vaccinated animals. Collectively, these findings establish the CD46/DSG-2 transgenic mouse as a physiologically relevant and translationally valuable model for HAdV-55 infection and demonstrate that iHAdV-55 vaccination confers robust humoral immunity and protective efficacy. This platform provides a critical tool for the development and preclinical evaluation of adenovirus-targeted vaccines and therapeutics.