Objective. This paper examines whether the effects of spousal coparenting on authoritative parenting are mediated through parenting stress. Design. A total of 166 married, heterosexual couples in Hong Kong with a preschool child provided information about their spouse's level of cooperation and triangulation in their coparenting relationship at Time 1; their own parenting stress at Times 1 & 2; and their authoritative parenting at Times 1, 2, and 3. Results. Cooperation at Time 1 affected fathers' authoritative parenting at Time 3 completely mediated through fathers' parenting stress at Time 2. There were no mediated or direct effects on authoritative parenting for mothers, although triangulation at Time 1 predicted mothers' parenting stress at Time 2. Conclusion. Parenting stress mediates the relation between coparenting and authoritative parenting for fathers, suggesting the need to encourage cooperation from mothers. In this way fathers' stress related to their role as parent will decrease, helping to promote their authoritative parenting. Copyright © 2019 Taylor & Francis Group, LLC.