Purpose: The study aims to examine the effectiveness of a positive psychology group-based intervention program, incorporating elements of hope and gratitude, in decreasing depression and increasing life satisfaction among primary school students in Hong Kong. Method: A total of 68 children, with the Depression score of Chinese Hospital Anxiety and Depression Scale from 9 to 11, were randomly assigned to the intervention and control groups. An eight-session intervention group-based program was conducted in five primary schools. Results: Participants of the intervention groups showed a significant decrease in depression and significant increase in life satisfaction, partially mediated by hope and gratitude, after the intervention when compared with those of the control groups. Discussion: As positive psychology intervention teaches children ways to increase their positive cognition, emotions, and behaviors, it may help children cope with current emotional problems and enhance their capability to deal with future stress and adversities.