[en] Mannose binding lectin (MBL) is a collagenous C-type lectin, which plays an important role in innate immunity. It can bind to carbohydrates on the surface of a wide range of pathogens, including viruses. Here we studied the antiviral effect of recombinant chicken (rc)MBL against Infectious Bronchitis Virus (IBV), a highly contagious coronavirus of chicken. rcMBL inhibited in a dose-dependent manner the infection of BHK-21 cells by IBV-Beaudette, as detected by immunofluorescence staining of viral proteins and qPCR. ELISA and negative staining electron microscopy showed that rcMBL bound directly to IBV, resulting in the aggregation of viral particles. Furthermore, we demonstrated that MBL bound specifically to the spike S1 protein of IBV which mediates viral attachment. This subsequently blocked the attachment of S1 to IBV-susceptible cells in chicken tracheal tissues as shown in protein histochemistry. Taken together, rcMBL exhibits antiviral activity against IBV, based on a direct interaction with IBV virions. - Highlights: • Recombinant chicken MBL (rcMBL) has antiviral activity against IBV-Beaudette in cell culture. • rcMBL aggregates IBV virus-particles. • rcMBL binds through its carbohydrate recognition domain to the S1 spike protein of IBV. • rcMBL can prevent binding of IBV-S1 to chicken tracheal tissues.