Introduction Emotional disorders (anxiety and depressive disorders) are a relevant public health concern associated with high prevalence, high costs, and important disability. Therefore, research priorities include designing and testing cost-effective interventions to reach everyone in need. Internet-delivered interventions for emotional disorders are effective and can help to disseminate and implement evidence-based treatments. However, although these treatments are generally effective, not all patients benefit from this treatment format equally. Blended treatments are a new form of intervention that combines the strengths of face-to-face and Internet approaches. Nevertheless, research on blended interventions has focused primarily on individual therapy, and less attention has been paid to the potential of using this format in group psychotherapy. This study aims to analyze the feasibility of blended transdiagnostic group CBT for emotional disorders. The current article describes the study protocol for this trial. Method and analysis A one-armed pilot trial will be conducted. Participants will be 30 adults suffering from DSM-5 anxiety and/or depressive disorders. The treatment consists of a blended transdiagnostic group intervention delivered during a period of 24 weeks. Groups of 6 to 10 patients will attend a total of eight 2-hour, face-to-face sessions, alternated with the use of an online platform where they will find the contents of the treatment protocol. The intervention has four core components: present-focused awareness, cognitive flexibility, identification and modification of behavioral and cognitive patterns of emotional avoidance, and interoceptive and situational exposure. These components are delivered in 16 modules. Assessments will be performed at baseline, during the treatment, at post-treatment, and at 3-month follow-up. Clinical and treatment acceptability outcomes will be included. Quantitative and qualitative data (participants' views about blended group psychotherapy) will be analyzed. Ethics and dissemination The trial has received ethical approval from the Ethics Committee of Universitat Jaume I (September 2019) and will be conducted in accordance with the study protocol, the Declaration of Helsinki, and good clinical practice. The results of this study will be disseminated by presentation at conferences and will be submitted for publication in a peer-reviewed journal. Trial registration ClinicalTrials.gov Identifier: NCT04008576. Registered 05 July 2019, https://clinicaltrials.gov/ct2/show/NCT04008576