Geotextile/geomembrane composite was made to improve the protection function of geomembrane as water barrier and its geosynthetic related properties for flexible membrane liner of waste landfill system were examined. Polypropylene needle-punched nonwoven geotextile and high density polyethylene geomembrane were used as raw materials and thermal bonding method was used to bind these materials. Tensile strength values of this geocomposite in machine and cross directions increased but tensile strain values decreased compared with those of geomembrane. Tear, puncture, and bursting strength values of this geocomposite increased by thermal bonding. Friction property between geocomposite/conducted soils interfaces of this geocomposite measured by direct shear test was improved. For chemical stability the changes of tensile strength and strain were in the range of -20~10% but those of tensile strain were smaller than those of tensile strength. The chemical treatment temperatures had no effect on the changes of tensile properties.