The long-term sustainment of bullying prevention programs has rarely been investigated. This study addresses this gap by identifying facilitators and barriers to the systematic implementation of KiVa antibullying program in real-life conditions, after an evaluation trial. The study is based on focus group interviews with teachers from 15 Finnish primary schools implementing the KiVa program. The schools were selected based on the annual KiVa survey data, with the criteria of long-term involvement in delivering the program and reaching successful outcomes in terms of decreasing trends in bullying and victimization. By utilizing thematic analysis, we identifed program-related, organizational, and contextual facilitators and barriers to sustainability. The results stress the importance of organizational factors in promoting program sustainability