Various studies have shown the associations between individual differences in human behavioral traits and genetic polymorphism of neurotransmitter-related proteins such as receptor, transporter and monoamine oxidase. To insight the genetic background of animal behavior, corresponding regions in animals have been analyzed. Especially the study has been promoted in dogs as the socially closest animal to humans. In dogs allele distributions of several genes were different among breeds showing different behavioral traits, and genes associating individual difference in aggressiveness and aptitude of working dogs were surveyed. The survey of behavior-related genes is also carried out in other mammals such as primates, horses and cetaceans and also in birds. The marker genes for behavior will provide useful information for better relationship with companion dogs and effective selection of working dogs.