A special relationship between human and dog is considered to be established by dog's characteristic social skill and cognitive ability, based on adequate emotional and affiliative behavior. It has been emphasized that puppy's experience in its developing period is prerequisite for dog's socialization to human. On the other hand, it is also indicated that if maternal environment is deprived, it would cause various behavioral problems of impairing dog's sociality in adulthood, such as anxiety, fear-related behavior, or aggression toward human. These suggest that maternal environment in dogs could have a large impact on the human-dog relationship. In various mammalian species including human, the quality of mother-infant relationships has been shown to affect neurobehavioral development related to sociality. However, there are few studies in dogs. This article discusses how dog's sociality can be influenced by maternal environment in each developmental stage of puppy, and underlying predictable mechanisms for it. The developmental approach to dog's sociality will be beneficial for better understanding of a special relationship between human and dog.