Psychological flexibility (PF) refers to an individual’s capacity to deal with the present moment non-judgmentally and to commit to value-based actions. This study evaluated how parental PF, psychological adjustment to a child’s illness, and psychological symptoms including anxiety, depression, and stress in parents are associated with asthma morbidity in children. Three-hundred and twenty-four parents of children aged 3–12 years with asthma completed a self-administered questionnaire to measure their PF, psychological adjustment, and symptoms of anxiety, depression, and stress, their children’s asthma symptoms and their use of bronchodilators. Structural equation modeling was used to explore the relationships among these constructs. The results showed that poor PF was significantly associated with poor psychological adjustment to the child’s illness and increased psychological symptoms in parents. Parental PF was found to be the only latent construct possessing a significant association with the child’s asthma morbidity (β = 0.27, 95% CI [0.09, 0.42], p = .002). These results suggest that by fostering their PF parents may improve their own psychological well-being as well as their child’s asthma condition.