Introduction.Moraxella bovoculi is frequently isolated from the eyes of cattle with infectious bovine keratoconjunctivitis (IBK; pinkeye). As with M. bovis, which has been causally linked to IBK, M. bovoculi expresses an RTX (repeats in the structural toxin) cytotoxin that is related to M. bovis cytotoxin. Pilin, another pathogenic factor in M. bovis, is required for corneal attachment. Seven antigenically distinct pilin serogroups have been described in M. bovis.Hypothesis/Gap Statement. Multiple different serogroups exist amongst type IV pilin encoded by M. bovis, however, it is not known whether M. bovoculi exhibits a similar degree of diversity in type IV pilin that it encodes.Aim. This study was done to characterize a structural pilin (PilA) encoded by M. bovoculi isolated from cases of IBK to determine if diversity exists amongst PilA sequences.Methodology. Ninety-four isolates of M. bovoculi collected between 2002 and 2017 from 23 counties throughout California and from five counties in four other Western states were evaluated.Results. DNA sequencing and determination of deduced amino acid sequences revealed ten (designated groups A through J) unique PilA sequences that were ~96.1-99.3 % identical. Pilin groups A and C matched previously reported putative PilA sequences from M. bovoculi isolated from IBK-affected cattle in the USA (Virginia, Nebraska, and Kansas) and Asia (Kazakhstan). The ten pilin sequences identified were only ~74-76 % identical to deduced amino acid sequences of putative pilin proteins identified from the previously reported whole-genome sequences of M. bovoculi derived from deep nasopharyngeal swabs of IBK-asymptomatic cattle.Conclusions. Compared to the diversity reported between structural pilin proteins amongst different serogroups of M. bovis, M. bovoculi PilA from geographically diverse isolates derived from IBK-affected cattle are more conserved.