Coping with academic demands can be challenging for university students with Attention-Deficit/Hyperactivity Disorder (ADHD). Treatment can help them cope and prevent related mental health issues. The present study aimed to investigate the feasibility of a randomized controlled trial for group Cognitive Behavioural Therapy (CBT), including the use of an app for CBT homework assignments, and to explore the effects of CBT for university students with ADHD. University students (n = 36) participated in the first phase of the study, involving the design of an app to present CBT homework assignments, by evaluating prototypes of the app along with the development team. In the second phase, a pre- vs. post-test design was used. Students with ADHD (n = 7) were offered manual-based CBT once a week for 6 weeks using the app or a paper manual to do the homework, as preferred. University students who took part in the development of the app noted that they would rather use the app than a printed manual. On the other hand, participants in the CBT feasibility study preferred doing homework on paper rather than using the developed app. They all found group CBT and the key elements in the CBT manual helpful. The findings suggest that providing group CBT for university students with ADHD through 6 sessions is feasible and assessing its effects in a randomized controlled trial (RCT) is feasible. Such treatment might improve coping with ADHD symptoms and related mental health issues. Further studies on the development of an app supporting CBT are needed.Trial registration Registry name: Cognitive Behavioural Therapy for University Students with Attention-deficit Hyperactivity Disorder (ADHD). URL: https://register.clinicaltrials.gov. Registration number: NCT 04714866.