Objective To assess whether a practical intervention based upon a smartphone application (app) would improve self‐management and seizure control in adults with epilepsy. Design, setting Randomised, controlled trial in western China, December 2017 to August 2018. Participants 380 eligible people with epilepsy were recruited; 327 completed the 6‐month follow‐up (176 in the app group, 151 in the control group). Main outcome measures Self‐management of epilepsy (measured with the validated Chinese Epilepsy Self‐Management Scale, C‐ESMS) and self‐reported seizure frequency. Results In the intention‐to‐treat analysis, the mean C‐ESMS score increased significantly in the app group between baseline and the 6‐month evaluation (from 121.7 [SD, 12.1] to 144.4 [SD, 10.0]; P < 0.001); improvements on the information management, medication management, and safety management subscales were also statistically significant. At 6 months, the mean overall C‐ESMS score for the app group was significantly higher than that for the control group (125.4 [SD, 1.5];  P < 0.001). The proportion of patients who were seizure‐free at the 6‐month follow‐up was larger for the app than the control group (54 of 190, 28% v 22 of 190, 12%), as was the proportion with reductions in frequency of between 75 and 100% (22 of 190, 12% v 8 of 190, 4%). Changes in C‐ESMS score were not statistically associated with seizure frequency. Conclusions Using a smartphone app improved epilepsy self‐management scores in people in western China. It should be further tested in larger populations in other areas. Our preliminary investigation of building digital communities for people with epilepsy should encourage similar approaches to managing other chronic diseases. Trial registration Chinese Clinical Trial Registry, ChiCTR1900026864, 24 October 2019.