Abstract Background Cognitive behavioural therapy (CBT) is the most widely recognised and efficacious psychological therapy for the treatment of anxiety disorders in children and adults. However, suboptimal remission rates indicate room for improvement in treatments, particularly when both children and their parents have anxiety disorders. Bidirectional transmission and maintenance of anxiety within parent–child dyads could be better targeted by CBT, to improve treatment outcomes for children and parents with anxiety disorders. This study aimed to develop and evaluate the feasibility and acceptability of a concurrent parent–child enhanced CBT intervention that targets the individual’s anxiety disorder(s), as well as the bidirectional factors that influence and maintain anxiety in the dyad. Methods Feasibility and acceptability of the proposed CBT protocol will be evaluated in an open-label pilot trial of the intervention utilising qualitative and quantitative data collection. Ten parent–child dyad participants (n = 20) with anxiety disorders will be recruited for the proposed intervention. The intervention is based on an empirically supported 10-week CBT programme for anxiety disorders in adults, adapted to be delivered to parent–child dyads concurrently, and to target anxious modelling and overprotective behaviours through joint observational exposures. Intervention feasibility will be explored by pre-post symptom change on a range of clinician- and self-report measures to determine preliminary indications of participants’ intervention response and effect size calculations to estimate sample size for a future definitive randomised controlled trial (RCT). Additional feasibility measures will include recruitment rates, completion rates, and adherence to programme requirements. To explore participant acceptability of the intervention, qualitative interviews will be conducted with five parent–child dyads who complete the intervention (n = 10), along with five parent–child dyads with anxiety symptoms who express interest in the intervention (n = 10). Acceptability measures will include prospective and retrospective quantitative self-report and qualitative interview data. Discussion This pilot trial will utilise a mixed-methods design to determine the feasibility and acceptability of delivering an enhanced CBT intervention for the concurrent treatment of parent–child dyads with anxiety disorders. The results of this trial will inform the development and implementation of a future definitive randomised clinical trial to evaluate intervention efficacy. Trial registration Australian and New Zealand Clinical Trials Registry, ANZCTR1261900033410. Prospectively registered: pre-results. Registered 04 March 2019.