Background: For pediatric oncology patients and their parents, Fear of Progression (FoP) is a main psychosocial burden. We developed an intervention and examined its effectiveness in a small sample. Methods: 29 families with a child with cancer in acute treatment or follow-up care and elevated FoP-levels participated. The intervention consists of psychoeducation, anxiety confrontation, and resource activation and is proofed in a randomized control study with a wait list group who received treatment as usual (tau). All participants completed questionnaires on FoP and secondary outcomes (e.g. depression) at different time points. We calculated Mann-Whitney-U-tests for between as well as Friedman and Wilcoxon tests for within group comparisons. Multiple regression was used to explore differential effectiveness. Results: There was a significant difference in FoP after intervention/tau between the two groups (W=65.5, p=.023) with high effect size (g=-0.855, 95% CI [-1.596;-0.115]). The pre-post and follow-up comparison showed that parental (χ²[2]=24.14, p<.001, ω=0.377, CI [0.18;0.62]) and child’s (χ²[2]=24,14, p<.001, ω=0.124, 95% CI [0.19;0.62]) FoP differed between the measurement points but only for parental FoP post-hoc tests revealed a decrease after intervention (W=462.5, p<.001, g=0.855; 95% CI [0.517;1.193]) and follow-up (W=503, p<.001, g=0.893; 95% CI [0.586; 1.218]). Time since diagnosis may influence the intervention effect (β=-0.447; p=.004). Discussion: The intervention can reduce parental FoP and seems promising for children. A major limitation of our study is the small sample size. Conclusion: The intervention represents an initial approach to treat elevated FoP in pediatric oncology. Retrospectively registered at the German Trail Registry (TRN: DRKS00024106, 04.05.2022).