Directional asymmetry (DA) appears when the left and right body sides differ consistently from each other. This asymmetry is characterized as a type of natural asymmetry typical of the population's biology, which can be derived both from genetic inheritance, as of the functional importance acquired by certain features with respect to the environment in which they develop. We report here preliminary findings that for the first time to quantify size asymmetry mandibles of companion rabbits. A total sample of 64 companion rabbits from the same farm were studied by means of geometric morphometric techniques. The mandible morphology was described by a set of 18 landmarks and semil and marks on the lateral aspect. Tests showed paired differences with variations in distributions, demonstrating a DA in favour of left mandibular side. The detected unilaterality could be interpreted as a manifestation of lateralized masticatory activity. This is a first time report to quantify size asymmetry in this species.