Abstract: Bowlby's attachment theory explains the child's tie to the mother from an evolutionary perspective, postulating that attachment behaviors such as crying and following are species-wide characteristics guided by an innate “attachment behavioral system.” These behaviors normally elicit caregiving behaviors serving to protect the child from danger. Ainsworth's separation-reunion laboratory procedure known as the “strange situation” (SS) was invented to estimate the secure vs. insecure quality of the parent-infant attachment relationships. Three patterns of attachment emerged, “secure,” “insecure-avoidant,” and “insecure-ambivalent/resistant.” Numerous SS studies have replicated Ainsworth's finding that most infants are securely attached to the parent. In the mid 1980's, however, one study conducted in Japan reported that only the “insecure-ambivalent/resistant” pattern appeared in the insecure group, and hence the applicability of the SS in Japan was questioned. Some later claimed that attachment security in Japan is characterized by “dependency” with presumed emphasis upon absence of exploratory behaviors based on the Japanese concept of amae. Hence, it was proposed that what Westernized cultures term “insecure-ambivalent/resistant” might actually represent the ideal form of security in Japan. Japan has been therefore considered a “challenge” for attachment researchers. A strong link has been found between parental responses to the Adult Attachment Interview (AAI) and infants' attachment status. Additionally, infants' SS responses to a given parent have been found highly predictive of 6-year-olds' reunion responses to the same parent. This study pioneers an investigation of the intergenerational transmission of attachment between Japanese mothers and their 6-year-olds. The AAI was administered to 42 Sapporo mothers and mothers' attachment security vs. insecurity was estimated based on how coherently they spoke about their childhood experiences according to the AAI classification system (Main, Goldwyn, Hesse, 2002). Children's attachment security vs. insecurity was assessed via the Main-Cassidy sixth-year reunion system. For the majority of analyses, I found distributions of classifications for both adults and 6-year-olds comparable to the global distribution, i.e., the majority were secure, with both types of insecure categories represented. Furthermore, a strong match of attachment status was found between Japanese mothers and their 6-year-olds, even to the level of sub-classification.