Purpose: This study examined the efficacy of a 10-week internet-based cognitive behavioral therapy (iCBT) program “REST Online” for Hong Kong university students with mild to moderate levels of psychological distress. Method: A total of 206 Hong Kong university students were randomized into: (1) web-based and (2) app-based iCBT, and (3) waitlist control (WLC) groups. Results: Compared with the WLC group, the participants in the two iCBT groups showed a significant reduction in psychological distress, depression and anxiety symptoms, and negative thoughts and emotions, and significant increase in positive thoughts and emotions, with medium to large effect sizes. The positive effects were sustained at the 3-month follow-up test. No significant intervention effects were found between the two iCBT groups except for anxiety symptoms. Discussion: The findings were discussed in terms of program design and service delivery, and suggestions for delivering digital mental health service in Hong Kong universities were proposed.