Background: Up to 70% of cancer survivors report clinically significant fear of cancer recurrence (FCR). This parallel RCT evaluated the impact of a psychological intervention, Conquer Fear (CF), on FCR in cancer survivors. Methods: Participants were disease-free stage I-III breast, colorectal or melanoma cancer survivors, 2 months to 5 years post-treatment, who scored above the clinical cut-off (≥13) on the FCR Inventory (FCRI) severity subscale. CF included 5 sessions incorporating attention training, detached mindfulness, challenging unhelpful metacognitions, values clarification and psycho-education. Participants were randomised to the intervention (n= 121) or a relaxation training (RT) control arm (n= 101) (target n= 260). The primary end-point was reduction in FCR (FCRI total) immediately after intervention completion. Follow-up assessments occurred immediately, 3- and 6-months post-treatment. Data analysis was by intention to treat. The differences in change in FCR from baseline between CF and RT and secondary outcomes were tested using independent t-tests. A difference of 14.5 points in FCR was considered clinically significant. Long-term changes in FCR and secondary outcomes were evaluated using linear regression models fitted with generalized estimating equations (GEE), adjusted for baseline FCR. Results: Reduction in FCR between baseline and immediately post-treatment was significantly more in CF participants compared to RT. (Difference in change (95% CI): -10.5 (-16.1, -4.9); p < 0.001). Greater FCR reductions were also observed amongst CF participants at 3 months (-7.6 (-13.9, -1.4), p = 0.02) and 6 months (-7.8 (-14.2, -1.4), p = 0.02) compared with RT. The pattern of change in outcomes over time was consistent between treatment groups as no significant linear trends in treatment effects over time were observed. Conclusions: Conquer Fear is a theoretically-grounded intervention to reduce FCR and its associated psychological morbidity which leads to significantly greater reductions in FCR in the first 6 months following treatment than relaxation training. Clinical trial information: ACTRN12612000404820.