Kin-directed affiliative behavior is widespread in social animals and kin selection theory suggests that such behavior increases fitness of the performer and is thus adaptive. Allopreening in birds is an altruistic behavior as it involves cleaning body parts that cannot be cleaned by selfpreening. In this study, we investigated the effects of genetic relatedness on allopreening behavior among juveniles of the Bengalese finch Lonchura striata domestica shortly after the cessation of parental care. Nestlings were cross-fostered in order to distinguish the effects of genetic relatedness (sharing genetic parents) from the effects of familiarity (sharing rearing environment). Preening bouts toward siblings were more frequent and of longer duration than toward non-siblings. The frequency and duration of physical contact within a preening bout did not differ between siblings and non-siblings. In addition, the frequency and duration of preening bouts did not differ between the juveniles that were reared by the same foster parents and between those that were not. Our results suggest that Bengalese finch juveniles recognized siblings and performed affiliative behavior based on genetic similarity rather than familiarity. ARTICLE HISTORY