According to emotion socialization theory, parent characteristics interact with child and contextual factors to influence parent responding to youth emotions, which impacts youth emotional reactivity and regulation. However, little is known about how treatments for youth emotional disorders, particularly those with significant parent intervention components, may impact parents’ own emotional reactivity and their responses to youth emotion. We investigated whether parents (N = 91) participating in a transdiagnostic treatment for youth emotional disorders experienced change in their own emotional reactivity (i.e., symptoms, distress tolerance [DT], emotion regulation), supportive responses to youth emotion (e.g., expressive encouragement), and unsupportive responses to youth emotion (e.g., punitive, minimizing). We also examined the relationship of these changes to treatment-related change in youth symptoms. Parent anxiety, depression, stress, DT, and cognitive reappraisal significantly improved from pre- to post-treatment. Unsupportive responses to youth emotions also decreased. Change in parent DT and baseline youth symptoms were the only significant predictors of parent-rated post-treatment youth anxiety and depressive symptoms when all variables were included in regression models. This is the first known investigation of changes in parent emotional reactivity and responses to youth emotions in response to a transdiagnostic treatment of emotional disorders for youth. Results support the beneficial impact of treatment involvement on parents’ own emotional reactivity and behaviors, as well as the potential importance of targeting parent DT to improve youth symptoms.