This work aims to fill gaps in the present knowledge of the structures of pectin from Opuntia ficus indica of potential importance. The results demonstrated that MAE associated with RSM can be an efficient and economic procedure for extracting pectin from OFI cladodes. The structures of water soluble pectin (WSP) were also determined. Biophysical analysis of WSP using HPSEC, light scattering and FTIR, shows that it¿s low methylated high molecular weight pectin. Biochemical structure of WSP was further developed for this purpose using, methanolysis, silylation, carboxyl reduction and GC/MS analysis. Bioactivity study demonstrates a potential in vitro antioxidant, proapoptotic and cell cycle arrest activities of heat modified pectin (HT-DWSP). The HT-DWSP shows a very promising free radial scavenging and chelating capacities compared to commercial standards. HT-WSP cytotoxic activity is affecting selectively cancer cells, without any effect on normal ones.