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For thousands of years, collagen materials, such as leather, have been among the most dominant natural fibrous materials used by humans. Fatliquoring is one of the critical steps in the leather-making process, wherein oil or a lubricant is added to the leather to prevent the leather fibers from sticking together, thereby providing sufficient pliability to the leather. We have examined the feasibility of using the acoustic emission (AE) technique to characterize the degree of lubrication of leather produced with various fatliquor concentrations. In a tensile test, an acoustic transducer was contacted with the leather samples to collect their AE quantities and properties. The samples lubricated with a fatliquor concentration less than 10% showed twin peaks on the plot of hits rate versus time. This implied that a non-uniform fracture occurred in a leather structure that was not sufficiently lubricated. In contrast, a sufficiently lubricated leather structure showed a steady increase in hits rate with time unti l it fractured. Traditional stress-strain tests did not reflect these behaviors. Observations also showed a direct correlation between the cumulative hits and fatliquor concentration. The results of this work may provide a route to identify an adequate degree of lubrication in the leather.