The effects of proteolytic digestion on bovinesubmaxillary mucin (BSM) were investigated in terms ofchanges in size, secondary structure, surface adsorption, and lubricating properties. Two proteases with distinctly different cleavage specificities, namely trypsin and pepsin, were employed. SDS-PAGE analysis with staining for proteins and carbohydrate moieties showed that only the unglycosylatedterminal regions of BSM were degraded by the proteases. Size exclusion chromatography (SEC) and dynamic light scattering(DLS) analyses indicated that tryptic digestion mainly led to the reduction in size, whereas pepsin digestion rather caused an increase in the size of BSM. Less complete cleavage interminal peptide regions by pepsin and subsequent aggregation were possibly responsible for the increased size. Far-UV circulardichroism (CD) spectra of the protease-treated BSM showed a slight change in the secondary structure owing to the removal ofterminal domains, but the overall random coil conformation adopted by the central glycosylated domain remained dominant and essentially unchanged. Surface adsorption properties as characterized by optical wave guide light mode spectroscopy (OWLS) showed that tryptic digestion of BSM resulted in a decrease in the adsorbed mass, but pepsin digestion led to a slight increase inthe adsorbed mass onto a hydrophobic surface compared to intact BSM. This is in agreement with the partial preservation of peptide segments in the terminal regions after pepsin digestion as confirmed by SEC and DLS studies. Despite a contrast in the adsorbed amount of the protease-treated BSMs onto the surface, both proteases substantially deteriorated the lubricating capabilities of BSM at a hydrophobic interface. The present study supports the notion that the terminal domains of BSM are critical to the adsorption and lubricating properties of BSM at hydrophobic interfaces.