ABSTRACT This study examines the prevalence and effects of hate speech propagation on WhatsApp groups in Nigeria. It also explores the role of WhatsApp group administrators (WGAs) in regulating it. Online passive participant observation method was used to collect data from sixteen purposively selected WhatsApp groups in Nigeria. Results indicate a high prevalence of gender, religious, political and ethnic hate speech in majority of the sampled WhatsApp groups. It also shows that hate speech generates tension and conflict among WhatsApp group participants. Moreover, the study reveals that most WGAs applied punitive measures against hate speech propagators. The findings advance the emerging area of online hate speech and brings to fore the conflict resolution, peacebuilding and third-party policing potentials of WhatsApp group administrators.