Objectives : To study the apoptosis effects of fermented Undaria pinnatifida extracts(FUP) against HCT-15 colon cancer cells. Method : By measuring cell proliferation, DNA fragmentation, cell cycle, morphology, and western blot from FUP, the study investigated the effects of the extractions had upon the HCT-15 colon cancer cells, and concluded that the inhibiting effects upon cells were induced by apoptosis. Result : FUP effectively inhibited the growth of HCT-15 colon cancer cells. After analyzing the DNA fragmentation, the study observed a DNA ladder, while examining the cells, and found an increase of sub-G1 hypodiploid cells. On the changes regarding the nucleus of the cells, a condensation of cells and chromatin, as well as an apoptotic body was clearly observed. By observing through western blot from FUP, the study found a decreased level of Bcl-2 from HCT-15 colon cancer cells, but the increased level of Bax and cleaved caspase-3, which as a result induced apoptosis, inhibiting the growth of HCT-15 colon cancer cells. FUP increased the natural death of HCT-15 colon cancer cells by the induction of apoptosis. FUP seemed to have no suppressing effect upon HL-60/MX2 cells. However, compared to the fucoidan, the study was able to clearly observe morphological changes of HCT-15 cells apoptosis, in a 1/2 concentration. Conclusion : FUP had antiproliferative effects on different kinds of cancer cells, while proving especially efficacious against colon cancer cells.