[en] The respiratory syncytial virus (RSV) is a major pathogen of the human species. This pneumovirus is a prominent cause of airway morbidity in children and maintains an excessive hospitalization rate despite decades of research. As involvement of a genetic vulnerability is a possibility supported by recent data, we addressed the question of whether the Mx gene products, the typical target of which consists in single-stranded negative-polarity RNA viruses, could alter the course of pneumovirus-associated disease in vivo. Wild-type and Bos taurus Mx1-expressing transgenic FVB/J mice were inoculated with the mouse counterpart and closest phylogenetic relative of RSV, pneumonia virus of mice. Survival data and follow-up of body weight, histological scores, lung virus spread and lung viral load unequivocally showed that the viral infection was severely repressed in Mx-transgenic mice, thus suggesting that pneumoviruses belong to the antiviral spectrum of mammalian Mx GTPases. Elucidating the underlying mechanisms at the molecular level could reveal critical information for the development of new anti-RSV molecules.