Aims This study aimed to examine the impact of synchronous online learning on the effectiveness of theoretical training and self-efficacy among newly graduated pediatric nurses. Design It is a prospective randomized controlled trial. Methods The sample comprised 45 newly graduated pediatric nurses randomly assigned to an experimental cohort group or a cohort group. The control group underwent traditional face-to-face teaching, whereas the experimental group engaged in synchronous online learning. A comparative analysis encompassed the test scores from post-session 10-minute assessments (T2), evaluations conducted after one week (T3), and those after one month (T4), alongside their academic self-efficacy scores. Results Forty-five newly graduated pediatric nurses participated with 23 allocated to the control cohort and 22 allocated to the experimental cohort. The baseline characteristics revealed no statistically significant disparities between the two groups. The post-session 10-minute assessment (T2) revealed a slight, yet not statistically significant, advantage for the experimental group over the control group. However, in contrast, the experimental cohort exhibited significantly superior performance compared to the control group during theoretical evaluations conducted one week (T3) and one month (T4) after training (p<0.001). In terms of academic self-efficacy, the experimental group demonstrated significantly higher scores than their counterparts in the control group. Conclusions Synchronous online learning that is meticulously structured and closely monitored has the potential to enhance the efficacy of theoretical training and boost academic self-efficacy among new graduate nurses.