HIV/AIDS has remained a public health issue affecting both children and adults. Children including those in school settings are known to be at risk of contracting HIV/AIDS from numerous avenues which they may not have the knowledge. This study examined the effectiveness of rational emotive digital storytelling therapy (REDStory) on HIV/AIDS knowledge and risk perception among Nigerian schoolchildren. The design of the study was a group randomized trial design. A total of eighty schoolchildren participated in the study. For the collection of data, we utilized the HIV Knowledge Questionnaire (Carey and Schroder in AIDS Educ Prev 14:174–184, 2002) and the Perceived Risk of HIV Scale (Napper et al. in AIDS Behav 16(40):1075–1083, 2012). To analyze the collected data, we employed ANOVA with repeated-measures and t test statistics. The study post-treatment results showed that the REDStory intervention significantly improved the degree of knowledge and perception of risk of HIV/AIDS among the schoolchildren in the treatment group in comparison to those in the waitlisted control group. In addition, follow-up results showed that the schoolchildren in the treatment group maintained the significant effect which the REDStory intervention had on them with regard to improved knowledge and risk perception of HIV/AIDS. The study outcomes implies that the application of REDStory for improving knowledge and perception of risk of HIV/AIDS among Nigerian schoolchildren is beneficial and therefore warrants further clinical utility and adaptation.