We investigated how information about relatedness is coded in the anal gland secretion (AGS) of the beaver (Castor canadensis). Using gas chromatography, we found that individual secretion profiles did not change over time and location of the beaver and the variation in the AGS profile was smaller within an individual than between individuals. Therefore, the AGS is suituable for characterising individuality. We also found that related individuals shared more features in the AGS profile than did unrelated individuals. Hence, information about kinship can be coded in the AGS profile. These findings substantiate the behavioural kin recognition system using the mechanism of phenotype matching in the beaver.