Evidence-based early intervention programs for children at risk of developing psychological problems after exposure to armed conflict have been recommended as a major component in the treatment of psychosocial problems. This study examines the efficacy of a pilot school-based mindfulness intervention (SMI) and its impact on the social, emotional, and behavioral outcomes of war-affected refugee preschool children living in a refugee camp in Türkiye. A single-blind randomized controlled trial with pre-test and post-test design was employed. A total of 76 participants (born in 2013) were randomized by the school into the 6-week intervention (n = 38) or the control group (n = 38). Measures included the State Self-Esteem Scale, Early Childhood Social Skill Measure, and the Child and Youth Resilience Measure-Revised. GLM repeated-measures ANOVA (p < 0,05) analysis showed positive effects of SMI on social skills (F = 126.06, p < 0.05, η2 = 0.63), self-esteem (F = 72.08, p < 0.05, η2 = 0.49) and resilience (F = 4.33, p < 0.05, η2 = 0.05) over time for the intervention group as compared to controls. Significant reductions in social and emotional problems were found for children who reported high levels of introversion in the pre-test. Pilot study results support SMI as a promising intervention for psychosocial problems that can reduce stress and anxiety symptoms among children exposed to armed conflict and forced migration.