Oxytocin is mostly synthesized within the hypothalamus and acts mainly on the oxytocin receptor that is expressed in the nervous system and peripheral organs. Oxytocin exerts not only reproduction-related functions such as delivery of children and milk ejection during the lactation period, but also various actions including control of stress-related responses, emotional responses and social behaviour. [1][2][3][4][5][6][7] The oxytocin receptor gene has single-nucleotide polymorphisms (SNPs) and SNPs of the oxytocin receptor gene have been shown to be associated with difference in pair bonding, 8 empathy and stress responsiveness, 9 generous