Objective: The rhizome of Zingiber cassumunar is widely used as a folk medicine in Thailand. In this study, effects of Zingiber cassumunar derivatives on cellular proliferation and the expression of cell cycle-related proteins in oral cancer cell lines (HN4 & 12) were investigated. Materials and Methods: Dry rhizomes of Zingiber cassumunar were extracted with 95% ethanol with a Soxhlet apparatus for 6 h. DMPBD, compound D and compound B were isolated from the ethanolic extract of Zingiber cassumunar by TLC. Anti-proliferation properties of the test substances were determined using MTT assay and a flow cytometric analysis. Effects of Zingiber cassumunar and its derivatives on the expression of cell cycle related proteins, cyclin D1 and CDK4, in HN4 & 12 cells were determined using western blotting. Results: MTT assay demonstrated cytotoxicity of crude Zingiber cassumunar extracts, DMPBD, compound D and compound B in a concentration- dependent manner (50-150 microgram/ml). The tested substances could arrest the cell cycle progression of HN4 and HN 12 cells at the G0/G1 phase. However, a decrease of cyclin D1 and CDK4 was not observed in oral cancer cells treated with Zingiber cassumunar extracts, DMPBD, compound D or compound B for 48 h. Conclusion: Our results suggest that DMPBD, compound D and compound B derived from Zingiber cassumunar could inhibit cell cycle-related protein expression and resulted in cell cycle arrest in oral cancer cells.