BACKGROUND: People with a melanoma diagnosis are at risk of recurrence, developing a new primary or experiencing disease progression. Previous studies have suggested that fear of a cancer recurrence is clinically relevant in this group of patients and, if not addressed, can lead to distress. Mindfulness-based interventions have been shown to alleviate symptoms of anxiety and depression among various groups of cancer patients. Online mindfulness-based interventions have the potential to reach people unable to attend face-to-face interventions due to limitations such as cancer-related illness, transportation or time constraints. This study aims to (1) examine whether individuals with a melanoma diagnosis are willing to participate and adhere to a 6-week online mindfulness-based intervention and (2) explore potential benefits of the program on fear of cancer recurrence, worries, rumination, perceived stress and trait mindfulness to inform the design of a clinical trial. METHODS/DESIGN: This is a single-site randomised controlled trial of a feasibility study. Seventy-five participants with stage 2c or 3 melanoma will be recruited from a melanoma outpatient clinic and randomised (2:1) either to an online mindfulness-based program (intervention) or to usual care (control). The intervention is a 6-week program specifically developed for this study. It consists of videos describing the concept of mindfulness, short daily guided meditation practices (5-10 min), automated meditation reminders and instructions for applying mindfulness in daily life to enhance wellbeing. All participants will complete questionnaires at baseline and at 6-week post-randomisation. Participants in the control group will be given access to the online program at the end of the study. Primary outcomes are overall recruitment; retention; extent of questionnaire completion; and usability and acceptability of, and adherence to, the program. The secondary outcomes are fear of cancer recurrence, worries, rumination, perceived stress and trait mindfulness measured using validated instruments. DISCUSSION: This feasibility study will evaluate participants' satisfaction with the program and identify barriers to recruitment and adherence. The recruitment and data collection process will highlight methodological aspects to address in the planning of a larger scale study assessing the impact of an online mindfulness-based intervention on fear of cancer recurrence and wellbeing. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry, ACTRN12617000081314 . Registered on 16 January 2017.