The exclusive human pathogen Neisseria gonorrhoeae uses glycosylation on pili to mediate adherence to the I-domain of complement receptor 3 (CR3, CD11b/CD18, Mac-1). This receptor is expressed on primary human cervical epithelial (pex) cells. Surface plasmon resonance was used to characterize the interaction between the I-domain of CD11b and gonococcal pilin modified with a terminal galactose disaccharide, or a bacillosamine monosaccharide lacking the terminal galactose. No interaction was observed with the pilin-linked monosaccharide, but the terminal galactose disaccharide bound to recombinant CD11b I-domain (KD of 349 nM) and to full length CR3 (KD of 907nM). The role of the terminal galactose in this interaction was further verified using commercially sourced carbohydrates that terminate in α- or β-galactose with varying underlying linkages and sugars. We observed that a terminal galactose with any linkage was sufficient for binding to the I-domain with KD values ranging from 117 - 320 nM. Using an overlapping peptide library of the I-domain, the galactose-binding lectin domain was identified. A peptide called G2 was able to recapitulate the galactose-specific lectin activity of the full length CD11b I-domain. This domain was modelled and mutant peptides were created to verify the amino acids involved in galactose binding. The G2 peptide was able to block N. gonorrhoeae colonization in both CHO-CR3 and pex cell models of gonococcal adherence. The interaction between the CD11b I-domain and gonococcal pilin was mediated by terminal galactose binding to a small region of the I-domain, and this region was sufficient for inhibition of N. gonorrhoeae in human ex vivo models.