This study examined the effects of role lettering (RL) on mothers raising their first child in infancy. Mothers raising their first child in infancy experience unique childcare anxiety and are prone to mental instability. The Japanese government has set up support systems for mothers raising children, such as postpartum care programs; however, many of these require mothers to go out to seek support. Considering that mothers raising children are unable to go out easily, it is necessary to consider ways to provide support that are more convenient for mothers. We focused on RL as a method to support this. RL is a role-exchange letter method in which one writes a letter from the perspective of both oneself and others, in this case, the mother and the child, respectively. By conducting this back-and-forth correspondence alone, one encourages self-reflection. Putting oneself in another person's shoes allows one to look at oneself from a new perspective, promotes an understanding of the self and others, and encourages self-acceptance. This study hypothesized that RL could be utilized by mothers raising their first child, and if its effectiveness could be clarified, it could be used as a tool to support child-rearing. This paper consists of four sections. Chapter 1 presents the current situation and issues surrounding mothers raising their first child, a literature review on support for mothers raising their children, a literature review on RL, and the significance and purpose of this study. In Chapter 2, semi-structured interviews were conducted after RL was administered thrice to six mothers raising their first child before preschool. The data obtained were analyzed using the KJ method to structure the effects of RL. We also examined changes in the description of letters in the RL. In Chapter 3, we examine the effects of RL using a randomized controlled trial in a group of 26 mothers raising their first 0-year-old child in a group of three RLs and a control group. We also examined changes in the description of letters in the RL. Chapter 4 provides a comprehensive discussion of the effects of RL on mothers raising their first child during infancy based on the findings in Chapters 2 and 3. In sum, the effects of RL done thrice by mothers raising their first child in infancy are as follows. First, mothers write freely to the child, the letter recipient, without restrictions, thus express their feelings honestly; this naturally allows the mother to affirm her own identity. Second, by writing from the child’s perspective, the mother can think of how the child feels. These activities led to an increase in the mother’s self-esteem and positive feelings toward the child. Such a change in feelings gives the mother of a firstborn child a sense of recognition and confidence in her parenting. The results suggest that such confidence may lead to behavioral changes and willingness to connect with the outside world, such as mothers visiting places for parent-child interaction and consultation with public health nurses.