The purpose of this study was to examine how children self-regulate, related to their temperament and their mother's attitude toward the children's emotional expressiveness. The subjects were 359 mothers of 3-5 year old children in Seoul and Kyunggi-do. Chun’s Children's Temperament Measure (1992) was used to assess the children's temperament. Saarni's Parent Attitude toward Children's Expressiveness Scale (1990) was used to assess the mothers' attitude toward the children's emotional expressiveness. Also, Lee's Children's Self-regulation Measure (2003) was used to assess the children's self-regulation. The data were analyzed using Cronbach Alpha, two-way ANOVAs, Pearson's product moment correlations and stepwise multiple regression analysis. The main findings were as follows. There were significant differences in children's self-regulation by gender and age. There were significant differences in children's temperament in activity and reactivity by gender. Mothers accepted daughters with more sympathetic and empathic response when daughters expressed anxiety. Children's self-regulation was related to temperament and maternal attitude toward children's emotional expressiveness. Children's gender, reactivity, activity, adaptability, maternal attitude toward children's emotional expression of anger, and children's age were the variables that predicted self-regulation. These variables explained 37.1% of children's self-regulation ability.