<p>This study investigated the bidirectional associations between parenting stress and mastery motivation in preschoolers with typical development (TD). Participants included 102 Taiwanese preschoolers with TD aged 24–79 months and their mothers. Cognitive ability was assessed with standardized development/intelligence tests; mastery motivation with the Chinese version of the Revised Dimensions of Mastery Questionnaire; and maternal parenting stress with the Chinese version of Parenting Stress Index-short form. The results showed that Parent–Child Dysfunctional Interaction was the most important predictor of preschoolers’ mastery motivation, and Cognitive/Object Persistence and Social Persistence with Children were the most important predictors of maternal parenting stress. In conclusion, there is a bidirectional relationship between parenting stress and mastery motivation. This suggests that early childhood practitioners should assist parents in identifying and alleviating their parenting stress while fostering their child’s mastery motivation. Such efforts can help parents better understand their child’s strengths and weaknesses, ultimately supporting the child’s active participation in daily activities.</p>