Background: Durian (Durio zibethinus Linn.) has been shown to have cytotoxic activity in vitro. Objective: This study aimed to determine the efficacy of the Combination of both Doxorubicin and Durian Mesocarpium Ethanol Extracts (EEMD), a single concentration of Doxorubicin and Durian Mesocarpium Ethanol Extracts (EEMD) by examining in vitro to T47D cells line experimentally. Materials and Methods: The single and Combination concentration of both Durian Mesocarpium Ethanol Extracts (EEMD) and Doxorubicin were divided into three experimental groups to determine the IC₅₀ and Combination index. This assay was done using the MTT method. Results: The single concentration of Durian Mesocarpium Ethanol Extracts (EEMD) at 14.85 µg/ml, and the Combination of Durian Mesocarpium Ethanol Extracts (EEMD) and Doxorubicin at 3.5 µg/ml, showed a cytotoxic activity due to inhibiting the cell viability of T47D cells line. The Combination of 1/8 IC₅₀ Durian Mesocarpium Ethanol Extracts (EEMD) at  3.5 µg/ml with 1/8  and 1/4 IC₅₀ at 0.03 and 0.06 µg/ml Doxorubicin gave a strong synergistic effect with a percentage of cell viability (up to 64.57%) significantly (p<0.05) compared with the standard control. Conclusion: Based on these results, Durian (Durio zibethinus Linn.)  have a potential effect as a cytotoxic agent with CI values of combination Durian Mesocarpium Ethanol Extracts (EEMD), and Doxorubicin showed the strong to moderate synergistic effect (CI 0.1 – 0.9).

Key words: Durian Mesocarpium, Ethanol Extracts, Doxorubicin, T47D, IC₅₀, CI