This study investigated the influence on their mental well-being of the perinatal support given by Japanese grandmothers.The Rosenberg self-esteem and the Center for Epidemiologic Studies Depression (CES-D) scales were used to assess grandmothers’ mental well-being before and after their daughters’ childbirth. Of 198 grandmothers, 176 (88.9%) supported their daughters and three patterns of perinatal support were observed: grandmothers’ support at the grandparents’ house before childbirth (n = 95) (Satogaeri bunben; Japanese traditional perinatal support), grandmothers’ support at the grandparents’ house after childbirth (n = 53); and grandmothers’ support at the daughters’ house (n = 28).Those who supported their daughters at the grandparents’ house before childbirth – especially the middle-aged (less than 60 years old) – showed significantly lower scores of self-esteem. Scores of CES-D did not significantly change before and after childbirth in either subgroup of grandmothers. It was concluded that grandmothers play an important role in supporting their daughters, and Satogaeri bunben is a typical event in modern Japan. However, Satogaeri bunben is a burden for middle-aged grandmothers, and we need to support them.