Abstract: This study investigated the role of green tea extracts as a cytotoxic agent against human ovarian cancer cells in vitro using different concentrations of green tea extracts (20, 50,100 and 250 μg mL-1) for 24 h. In vitro proliferation assays were performed to compare the growth rate of all groups of cells. The numbers of viable cells were counted using Heamocytometer and Trypan blue staining (0.4%). The effect of green tea extracts was also studied for long period (24, 48 and 72 h) using the IC50 = 100 μg mL-1. The results of statistical analysis revealed significant decrease in the number of treated human ovarian cancer cells inversely proportion with increasing the concentration of green tea extracts, this experiments determined that the IC50 = 100 μg mL-1. In long term study, the results approved that there was significant reduction in the number of tumor cells by time in contrast with control none treated one. Morphologically, the images of the fixed and stained human ovarian cancer cells with Coomassie stain revealed that the Green tea extracts causing cells shrinkage, blabbing, chromatin condensation and loss of cell-cell contacts which were known as sign of apoptosis. In conclusion, green tea extract has been shown antiproliferative activity against the growth of HOCC which might be considered in clinical situation.