B Background: Cancer is a disease characterized by abnormal cell growth. Themost common type of cancer in oral cavity is squamous cell carcinoma, amalignant tumor of layered squamous epithelium. Tamarillo seed extract consistof phenolic compounds, flavonoids, triterpenoids, tannins, and alkaloids. Thosecompounds are known to have antioxidant, antiproliferative, anti-inflammatoryand anticancer activity. Tamarillo seed extract can inhibit the cell cycle in the G1 /S and G2 / M phases so the cell cycle will stop and give time for cells to repair thedamaged DNA. Aim: The aim of this study was to determine the effect of ethanolextracts of Tamarillo seed on HSC-3 cell viability. Method: This studyconducted using experimental research and in vitro laboratory, a treatment groupwhich divided into twelve groups namely tamarillo seeds extract withconcentration 40%, 20%, 10%, 5%, 2.5%, 1.25%, 0.625%, 0 , 3125%, 0.15625%,untreated cultures was a medium to used as negative controls, positive control of3% H2O2, and control of ethanol solvent 70%. Results: Concentration 5% ofTamarillo seed extract had a significant difference (p <0.05) compared to extractsat concentrations of 40%, 10%, 2.5%, 1.25%, 0.625%, 0.3125%, 0.15625%,negative control, and positive control. Conclusion: this study showed that the 5%concentration of Tamarillo seed extract is the lowest concentration that has thehighest ability to reduce cell viability. However, these concentrations have notbeen able to surpassed the inhibition of H2O2 as a positive control to reduce theability of HSC-3 cells to survive.