Background: Attention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental disorder in children and adolescents, characterized by attention deficit, hyperactivity, and impulsivity. Treatments for this population should be multidisciplinary and must be initiated as soon as possible. Non-pharmacological interventions for ADHD include psychoeducation, parent behavioural training programs and school interventions and accommodations. In response to the COVID-19 pandemic, we developed an online version of a combined psychoeducation and behavioural training program to facilitate access to mental health treatment and ensure continuity of care. The study assessed the acceptability of this online parent training program, among parents and/or caretakers of children and adolescents with ADHD. Methods: The program consisted of 10 online sessions over the course of 2 consecutive days (5 sessions a day). Satisfaction, usefulness and general comments about the program were assessed with open-ended questions and visual-analogous scales. Parents/caretakers’ use of strategies to manage behavioural problems was assessed using the Parenting and Family Adjustment Scales. Results: A total of 206 parents participated in the online program and 175 of them completed the evaluation. Overall, participants were satisfied with the content of the program and found it beneficial for their child. The engagement was high and no major obstacles were identified to participation, except some internet connection issues. More than half of participants had already used some of the strategies included in the program. Despite this, some difficulties in implementing new strategies were observed. Conclusions: Our study contributes to the growing body of papers evaluating online behavioral training program to improve their efficacy and content. With these measures, we hope to improve engagement in online psychoeducation and behavioural therapy programs. Future research evaluating online behavioural training programs should focus on ways to make them more accessible and adaptable to families’ obstacles.