Background Herbal remedies are increasingly popular for the treatment of functional dyspepsia. Chios mastic gum is a resinous exudate from the stem of Pistacia lentiscus var. chia. It is a traditional natural remedy used throughout the eastern Mediterranean. The aim of this study was to assess the efficacy of Chios mastic gum in patients with functional dyspepsia. Methods One hundred and forty eight patients fulfilling Rome II criteria for functional dyspepsia were randomly assigned to receive either Chios mastic gum 350mg three times daily or placebo. After 3 weeks of treatment the change from baseline in the severity of symptoms of functional dyspepsia was assessed using the Hong Kong index of dyspepsia. Patients’ global assessment of efficacy was also evaluated. Results The symptom score after treatment was significantly lower in the Chios mastic gum than in the placebo group ((14.78±1.78) vs (19.96±1.83)) (p <0.05). There was a marked improvement of symptoms in 40% of patients receiving placebo and in 77% of patients receiving Chios mastic gum (p <0.02). Individual symptoms that showed significant improvement with Chios mastic gum were: stomach pain in general, stomach pain when anxious, dull ache in the upper abdomen and heartburn (<0.05 for all four symptoms). Conclusion Chios mastic gum significantly improves symptoms in patients with functional dyspepsia compared to placebo.