Mobula kuhlii (Müller and Henle 1841) is a small species of devilray of the family Mobulidae. The species was recently uplisted to endangered on the IUCN Red List due to inferred population declines of >50% across much of its range. Here, we report aggregating behaviour of this little-known species at Pulau Si Amil, Sabah, Malaysia, in the western Sulawesi Sea. We report observations of schooling behaviour with encounters of groups of 20–100 individuals of M. kuhlii at Pulau Si Amil between May 2014 and July 2015. The limited reproductive output and low recovery rate of mobulid rays make these species particularly susceptible to overexploitation. It is therefore essential to identify areas of importance for these species in order to facilitate further research to delineate conservation and management plans.