Abstract Background Cognitive Behavior Therapy for psychosis (CBTp) effectively reduces positive symptoms, but the effects for delusions are small. Using approaches that focus on improving putative causal factors of delusions (emotion regulation (ER) and negative self-schemata) may be a way to improve CBTp for delusions. Objectives To pilot an emotion-focused CBTp intervention comprised of elements of different third wave approaches targeting ER and negative self-schemata (CBT-E) to investigate its feasibility and its potential efficacy. Methods A single-blind two-centered randomized wait-list controlled trial was performed. Patients with delusions in the context of a psychotic disorder (n=64) were randomized to CBT-E (treatment group (TG): n=35) or wait list (WL: n=29). TG received individual CBT-E in weekly sessions over six months, WL received CBT-E after a 6-months waiting time. Assessments were performed at baseline, after six months, and after 12 months. Results Rates of patients who consented and retained in CBT-E suggest acceptable feasibility and high acceptance of CBT-E. Multiple regression analysis in the intent-to-treat sample revealed no significant advantage in favor of TG in the primary outcome delusions (PSYRATS delusions), no effect on ER or negative self-schemata and a significant advantage in only one of the eight additional secondary outcome variables, namely general psychopathology. Discussion Although the intervention was feasible and acceptable, its effects on delusions did not hold up with the effects found for ‘targeted’ approaches in previous research and it needs to be improved to produce a stronger effect on the targets ER and self-schemata, before proceeding to a large-scale RCT.